Do you remember the name, Yuri Gagarin...the year was 1961 and this Russian cosmonaut was the first human to travel into space. After circling the earth, he came back and declared that he looked outside his capsule and didn’t see God anywhere. To which Dr. W. A. Criswell replied,

“Let him step out of his space suit for just one second and he’ll see God quick enough.”

Lloyd-Jones paraphrases this as...

"Blessed are those who are pure, not only on the surface but in the center of their being and at the source of every activity." (Lloyd-Jones, D. M. Studies in the Sermon on the Mount)

William Barclay picks up the thought of the Greek word for pure (see katharos below)...

Blessed is the man whose motives are always entirely unmixed, for that man shall see God. (W. Barclay, The Gospel of Matthew The New Daily Study Bible Westminster John Knox Press)

Isaac Watts has put this beatitude to hymn...

         I Hunger and I Thirst

Blest are the pure, whose hearts are clean
From the defiling powers of sin;
With endless pleasure they shall see
A God of spotless purity. (Play hymn)

Jesus' words in Matthew 5:8 answer the question

"How does one have 20/20 spiritual vision?"

Blessed (see makarios) means spiritually prosperous, independent of one's circumstances because it is a state bestowed by God and not a feeling felt. Fortunate, approved of God, happy independent of happenings. The Amplified Bible has this expanded definition for "blessed"

happy, enviably fortunate, and spiritually prosperous—possessing the happiness produced by the experience of God’s favor and especially conditioned by the revelation of His grace, regardless of their outward conditions" (Amplified Bible - Lockman)

Pure (2513) (katharos) means literally physically clean or pure and has the idea of unsoiled (free from dirt), unalloyed, without blemish, spotless, free from impure admixture or free from adulteration. Figuratively katharos was used in a ritual sense of food that was declared undefiled and thus acceptable (cf note Romans 14:20). In a moral or spiritual sense as used here by Jesus, katharos means to be free from corrupt desire or wrongdoing (sin and guilt) and thus pure or good in God's eyes (cf John 13:10 where Jesus was speaking figuratively, teaching that one who has been entirely cleansed, regenerated, possessing a new heart, born again, does not again need a radical renewal, but only needs to be cleansed from sins into which he falls each day, cf 1Jo 1:9). Katharos is to be free from admixture of what is false thus conveys the ideas of genuine, blameless or innocent.

As used in Mt 5:8, katharos describes a heart which is pure in motive and which exhibits single mindedness, undivided devotion and spiritual integrity. The idea is "This one thing I do" (as Paul said in Philippians 3:13 [note]). So although, "pure in heart" includes the ideas of moral purity or freedom from sensuality, that is not the primarily idea in the word katharos.

Pure (katharos) has to do with attitudes, integrity, and singleness of heart as opposed to duplicity and double mindedness (cf James 4:8). Thus, one might paraphrase Jesus' words in this beatitude as...

I desire a heart that is unmixed in its devotion and motivation. (Pure motives from a pure heart.)

Katharos gives us our English word catharsis which is used to describe a cleansing of one's mind or emotions.

Kent Hughes illustrates this idea of single mindedness writing that

Negatively, we can imagine this idea from everyday life if we reflect on those people who, having been introduced to us, keep talking and smiling, while at the same time looking behind and around us at other people and things. They really are not interested in us; they only see us as objects or a means to an end. In the God-man relationship such behavior is scandalous. Positively stated then, "pure" is represented by the words focus, absorption, concentration, sincerity, and singleness. "Blessed are the pure" is a searching statement, because focusing on God with a singleness of heart is one of the biggest challenges to twentieth-century Christians. Very few in this frenetic age are capable of the spiritual attention this Beatitude calls for. (Hughes, R. K. Sermon on the Mount: The Message of the Kingdom. Crossway Books)

MacArthur writes that katharos

was often used of metals that had been refined until all impurities were removed, leaving only the pure metal. In that sense, purity means unmixed, unalloyed, unadulterated. Applied to the heart, the idea is that of pure motive-of single-mindedness, undivided devotion, spiritual integrity, and true righteousness. Double-mindedness has always been one of the great plagues of the church. We want to serve the Lord and follow the world at the same time. But that, says Jesus, is impossible (cf note Matthew 6:24, James 4:4, 4:8)... Christians have the right heart motive concerning God. Even though we often fail to be single-minded, it is our deep desire to be so... Paul’s deepest spiritual desires were pure, although the sin dwelling in his flesh sometimes overrode those desires. Those who truly belong to God will be motivated to purity... The deepest desire of the redeemed is for holiness, even when sin halts the fulfillment of that desire... Purity of heart is more than sincerity. A motive can be sincere, yet lead to worthless and sinful things... Sincere devotees walk on nails to prove their spiritual power. Others crawl on their knees for hundreds of yards, bleeding and grimacing in pain, to show their devotion to a saint or a shrine. Yet their sincere devotion is sincerely wrong and is completely worthless before God. The scribes and Pharisees believed they could please God by such superficial practices as tithing “mint and dill and cummin”; but they “neglected the weightier provisions of the law: justice and mercy and faithfulness” (Matt. 23:23). They were meticulously careful about what they did outwardly but paid no attention to what they were inwardly...Even genuinely good deeds that do not come from a genuinely good heart are of no spiritual value. Thomas Watson said, “Morality can drown a man as fast as vice,” and, “A vessel may sink with gold or with dung.” Though we may be extremely religious and constantly engaged in doing good things, we cannot please God unless our hearts are right with Him. (MacArthur, J: Matthew 1-7 Macarthur New Testament Commentary Chicago: Moody Press this resource is highly recommended. Read his entire discussion on purity of heart) (See also online Happy are the Holy Matthew 5:8)

The TDNT sums up the usages of katharos as pertaining to...

physical, religious, and moral cleanness or purity in such senses as clean, free from stains or shame, and free from adulteration... In Primitive Religion. Ideas of power are dominant in primitive thinking about cleanness. After coming into contact with power, e.g., in birth, sex, and death, cleansing is necessary to fit one for ordinary life...In Greek Religion. At its primitive stage Greek religion follows the customary pattern. At the historical stage, however, the gods are seen as friendly forces, though they must be approached with cultic purity....The Old Testament  reflects the same general development. Uncleanness, which may be contracted in contact with birth or death (Lev. 12; Num. 19:11), is a positive defiling force. So is anything linked to a foreign cult...Stress also falls, however, on the holiness of God, so that the concept of purity develops with special force. Purifications by washing, sacrifice, or transfer restore forfeited purity and open up access to God. (Kittel, G., Friedrich, G., & Bromiley, G. W. Theological Dictionary of the New Testament.  Grand Rapids, Mich.: W. B. Eerdmans)

In classical Greek katharos described a river who course was "clear and open". In a moral or ethical sense the Greeks used katharos to describe one "clear from shame", "clear of guilt", of persons who purified after pollutions (even to the pagan Greeks touching a dead body cause one to be polluted). Katharos legally described one's state of being "clear of or from" a charge. Katharos was used to describe water which was "clear of admixture" and so "clear" or "pure". It was used to describe an individual's birth as "pure" or "genuine" and thus "citizens who were of pure blood". Herodotus used katharos to describe "the sound portion of the army", that is, that portion which was without blemish. The phrase "with clean hands" equated with "honestly". 

Katharos is used far more frequent in the Septuagint (LXX)  - 135 times! The first 8 uses describe "clean" animals (cf Ge 7:2-3, 8, 8:20), "pure" gold (cf the components inside God's Tabernacle! Ex 25:11,17, 29, 31, 36, 38, 39)

In the LXX of Genesis 20:5 we find a very interesting use of katharos. Abimelech had not gone into Sarah (who Abraham had lied about as being his sister) and so when confronted by God in a dream declared...

Genesis 20:5: "Did he (Abraham) not himself say to me, 'She is my sister'? And she herself said, 'He is my brother.' In the integrity (LXX = katharos for the Hebrew = tom = completeness, the quality or state of being complete or undivided as in our English term integer. Study the 7 uses in Psalms and uses in Proverbs and see if they don't relate to "purity of heart" as in this beatitude) of my heart and the innocence of my hands I have done this." 6 Then God said to him in the dream, "Yes, I know that in the integrity (LXX = katharos) of your heart you have done this, and I also kept you from sinning against Me; therefore I did not let you touch her." (Genesis 20:5-6)

Here is another interesting use of katharos in the LXX translation of Leviticus 7:19 (cf Lev 10:10, 11:36-37, 47, in fact 33 total uses of katharos for tahowr - see below - in the book of Leviticus)

'Also the flesh that touches anything unclean shall not be eaten; it shall be burned with fire. As for other flesh, anyone who is clean (LXX = katharos for the Hebrew tahowr = describes pure, clean animals and also that which is unalloyed) may eat such flesh.

Comment: The Hebrew Tahowr or "Clean" most frequently described the purity maintained by avoiding contact with other human beings, abstaining from eating animals, and using things that were declared ceremonially clean. Conversely, cleansing results if ritual procedures symbolizing the removal of contamination are observed. This latter "science" the Pharisees had made into an "art" with their emphasis on the external at the expense of the internal! Matthew 5:20 (note). The Pharisees liked the idea of “Blessed are the pure” as long as the statement stopped right there because they were the resident experts in outward purity. They had innumerable rules and regulations covering what you ate, what you wore, how far you could walk in the Sabbath, and so on. They scored an "A+" on being outwardly pure. But they flunked out on inward purity. To them this beatitude would be something like...

"Blessed are the outwardly clean, for they shall see God."

Jesus turned the tables on the Pharisees using their own vocabulary! To be pure in body is good. But to be pure in heart is best of all because it takes care of the external (in the right way). If you are pure in your heart, you will be pure everywhere. To be pure in heart then means to be pure from the inside out.

Look at Jesus' scathing pronouncement against the external purity without heart purity as practiced by the Pharisees in Mt 23:25-26, 27-28 declaring...

"Woe to you, scribes and Pharisees, hypocrites! For you clean (verb form katharizo) the outside of the cup and of the dish, but inside (their hearts were not pure)  they are full of robbery and self-indulgence.
26 "You blind Pharisee, first clean (verb form katharizo) the inside (first believe what your prophets wrote about "inner cleansing" = Ezekiel 36:26-27; 11:19-20, 18:31, cf Deut 30:6, Jeremiah 31:34, 32:39-40, Acts 15:9, 1Peter 1:22-23),: of the cup and of the dish, so that the outside of it may become clean also.
27 "Woe to you, scribes and Pharisees, hypocrites! For you are like whitewashed tombs which on the outside appear beautiful, but inside they are full of dead men's bones and all uncleanness. (akathartos - derived from the negative of katharos)
28 "Even so you too outwardly appear righteous to men, but inwardly you are full of hypocrisy and lawlessness.

Two more uses of katharos in the LXX are instructive, both in psalms by David (cf Acts 13:22)...

3 Who may ascend into the hill of the LORD? And who may stand in His holy place? 4 He who has clean hands and a pure (LXX = katharos) heart, who has not lifted up his soul to falsehood, and has not sworn deceitfully. (Psalm 24:3-4) (See notes Verse 3; Verse 4)

Create in me a clean (LXX = katharos for the Hebrew tahowr = describes pure, clean animals and also that which is unalloyed) heart, O God, And renew a steadfast spirit within me. (Psalm 51:10) (See Spurgeon's notes)

Finally in Ezekiel God promised that one day in the future (to be completely fulfilled at the return of Messiah at the end of the Great Tribulation)

Then I will sprinkle clean (LXX = katharos) water on you, and you will be clean (LXX = verb from katharizo > English "cathartic"); I will cleanse (katharizo) you from all your filthiness and from all your idols. 26 "Moreover, I will give you a new heart and put a new spirit within you; and I will remove the heart of stone from your flesh and give you a heart of flesh. (Ezekiel 36:25-26)

Katharos is the source of the English word catharsis, meaning purifying or cleansing. It is akin to the Latin castus from which we derive the word pure.

As alluded to above, from a biblical standpoint the concept of cleansing was deeply rooted in both the Old Testament, especially the Torah (the first five books of Moses). Under the Levitical laws heavy emphasis was placed on ceremonial cleansing. This forbade contact with unclean animals, substances, persons, or places. By the time of Christ this preoccupation with ceremonial cleanness had largely displaced true worship in Spirit and truth. Thus in this beatitude Jesus focuses in on a clean heart, rather than on ceremonial cleanness.

Charles Hodge rightly observed that

“Whenever true religion declines, the disposition to lay undo stress on external rites is stressed."

William Barclay explains that katharos but also had several meanings that help understand its use in this beatitude...

(i) Originally it simply meant clean, and could, for instance, be used of soiled clothes which have been washed clean.

(ii) It is regularly used for corn which has been winnowed or sifted and cleansed of all chaff.

In the same way it is used of an army which has been purged of all discontented, cowardly, unwilling and inefficient soldiers, and which is a force composed solely of first-class fighting men.

(iii) It very commonly appears in company with another Greek adjective—akēratos. Akēratos can be used of milk or wine which is unadulterated with water, or of metal which has in it no tinge of alloy.

So, then, the basic meaning of katharos is unmixed, unadulterated, unalloyed. That is why this beatitude is so demanding a beatitude. It could be translated: Blessed is the man whose motives are always entirely unmixed, for that man shall see God. So, then, a pure heart is a heart whose motives are absolutely pure and absolutely unmixed.

(Katharos)  it is commonly used in housing contracts to describe a house that is left clean and in good condition. But its most suggestive use is that katharos is used of that ceremonial cleanness which entitles a man to approach his gods. Impurity, then, is that which makes a man unfit to come before God, the soiling of life with the things which separate us from him.  (W. Barclay, The Gospel of Matthew The New Daily Study Bible Westminster John Knox Press)

Ray Pritchard gives us an excellent practical definition of purity of heart explaining that

Pure gold is not clean gold but 100%. Pure bread is all bread and no leaven. Pure water means that all the harmful elements have been removed by filtration. Some of you will remember when Ivory Soap advertised itself as being “99 and 44/100ths percent pure.” But in truth, anything less than 100% is not really pure! In this context being “pure in heart” means to have no double allegiance. Later on in the Sermon on the Mount Jesus warned against serving God and mammon (Matthew 6:24). No one can serve two masters at the same time. You will always love one and hate the other. And James 1:6-8  teaches us that the double-minded man is unstable in all his ways.

To be pure in heart means that you are sincere, transparent and without guile. What you see is what you get. No fakery, no trickery, no hypocrisy. I still remember hearing one of my Greek professors in seminary speak about Dr. John Walvoord, who was then the president of Dallas Seminary. He said, “You never have to wonder what Dr. Walvoord really means or if he’s trying to send you a double message. He is man without guile.” That statement has stayed with me across all these years because he’s the only man I’ve ever heard described in those terms. That statement reminds me of something I heard many years ago. A counselor said that he often tells his counselees, “You’re only as sick as your secrets.” The more you have to hide, the sicker you are. And if you’ve got a lot of secrets, you’re really sick.

Is your life an open book? Or do you have things that you hide from your best friends and from your loved ones? Is there anyone in your life who knows the truth about who you really are? Blessed are the pure in heart, for they have nothing to hide.  (Pritchard, R: The Tragedy of Double Vision) (Bolding added)

We must understand that God is far more interested in what we ARE than in what we DO for God. If what we are does not please His holiness, than what we do is virtually worthless. (cf 1Sa 16:7)

In his first letter to Timothy Paul wrote that (in contrast to the false teachers)...

the goal of our instruction is love from a pure heart and a good conscience and a sincere faith. (1Ti 1:5)

To have a pure heart fellowship and be accountable to those who have one...Paul says it this way (in his last written communication to Timothy)...

Now flee from youthful lusts, and pursue righteousness, faith, love and peace, with those who call on the Lord from a pure (katharos) heart. (see note 2 Timothy 2:22)

As yet we know Thee but in part;
But still we trust Thy Word,
That blessèd are the pure in heart,
For they shall see the Lord.

O Savior, give us then Thy grace
To make us pure in heart,
That we may see Thee face to face
Hereafter, as Thou art.
---John M. Neale (play)

Heart (2588) (kardia) (Click in depth study on kardia) is used figuratively most often in Scripture and refers to the center of each persons thoughts (mind) and will (see note by MacArthur below). The heart usually is more general referring to the inner person, the center of life, the volitional center of our being. The heart is the seat and "master control center" of human life. It is the center of your personality, the “real you” who makes the decisions of life. Thus, to be pure in heart is to be pure in the center of your life.

Jeremiah reminds us that unfortunately it is the heart that is source of all our troubles for...

"The heart is more deceitful than all else And is desperately sick; Who can understand it?' (Jeremiah 17:9)

Jesus echoes Jeremiah's assessment of the heart reminding us that...

"out of the heart come evil thoughts, murders, adulteries, fornications, thefts, false witness, slanders. These are the things which defile the man" (Matthew 15:19-20)

Why is the state of one's heart so important? In the Old Testament here are just a few reasons...

But the LORD said to Samuel, "Do not look at his appearance or at the height of his stature, because I have rejected him; for God sees not as man sees, for man looks at the outward appearance, but the LORD looks at the heart." (1 Samuel 16:7) (cf Acts 13:22 "...'I HAVE FOUND DAVID the son of Jesse, A MAN AFTER MY HEART, who will do all My will.' = single minded devotion and integrity just as Jesus calls for in this Sixth Beatitude) (Reputation is what others think about me. Character is what God knows is true of in my heart!)

"For the eyes of the LORD move to and fro throughout the earth that He may strongly support those whose heart is completely His..." (2Chronicles 16:9)

Watch over your heart with all diligence, for from it flow the springs of life. (Proverbs 4:23)

There is a certain "blessedness" inherent in the consciousness of a pure heart. (cf clean conscience - see suneidesis) A consciousness of a pure heart is a personal awareness of purity in our life. O the blessedness of those with a pure heart, the control center for all of your life.

God is far more interested in what we ARE than in what we DO for God. If what we are does not please His holiness, than what we do is virtually worthless. The heart is the center of the inner life of the person where all the spiritual forces and functions have their origin

FOR THEY SHALL SEE GOD:  hoti autoi ton theon opsontai (3PFMI):  (Genesis 32:30; Job 19:26,27; 1 Corinthians 13:12; Hebrews 12:14; 1 John 3:2,3)

BLEST ARE THE PURE IN HEART
Blest are the pure in heart,
For they shall see our God;
The secret of the Lord is theirs;
Their soul is Christ’s abode.

The Lord, who left the heavens
Our life and peace to bring,
To dwell in lowliness with men
Their Pattern and their King.

Still to the lowly soul
He doth Himself impart;
And for His cradle and His throne
Chooseth the pure in heart.

Lord, we Thy presence seek;
May ours this blessing be;
Give us a pure and lowly heart,
A temple meet for Thee.
---John Keble

As with the other beatitudes, In the Greek "they" is placed emphatically in the sentence signifying that it is "they and they alone" who will see God.  It is only the pure in heart, who shall Him for He reserves intimate knowledge of and fellowship with Him for those who maintain this purity of heart. How this should motivate us.

Spurgeon writes that...

It is a most blessed attainment to have such a longing for purity as to love everything that is chaste and holy, and to abhor everything that is questionable and unhallowed: There is a wonderful connection between hearts and eyes. A man who has the stains of filth on his soul cannot see God, but they who are purified in heart are purified in vision too: “they shall see God.”

See (3708) (optánomai from horao = to see) means to see with the eyes implying not just the mere act of physically seeing but also actual perception (act of coming to comprehend, grasp, attain awareness or understanding of) of what one sees.

Optanomai is used 4 times in 1 Corinthians 15 to describe Jesus' post-resurrection appearances (green = optanomai).

5 and that He appeared to Cephas, then to the twelve.
6 After that He appeared to more than five hundred brethren at one time, most of whom remain until now, but some have fallen asleep;
7 then He appeared to James, then to all the apostles;
8 and last of all, as it were to one untimely born, He appeared to me also. (see notes 1Corinthians 15:5; 15:6; 15:7; 15:8)

Optanomai is used repeatedly to refer to Jesus' Second Coming as shown in the following verses:

"And then shall appear the sign of the Son of man in heaven: and then shall all the tribes of the earth mourn, and they shall see the Son of man coming in the clouds of heaven with power and great glory" (Mt 24:30)

"hereafter you shall see THE SON OF MAN SITTING AT THE RIGHT HAND OF POWER" (Mt 26:64)

"Christ...shall appear a second time" (see note Hebrews 9:28)

"Beloved, now we are children of God, and it has not appeared as yet what we shall be. We know that, when He appears, we shall be like Him, because we shall see Him just as He is." (1John 3:2)

"BEHOLD, HE IS COMING WITH THE CLOUDS and every eye will see Him" (see note Revelation 1:7)

Here in Mt 5:8 "see" is in future continuous tense. In other words:

“They shall be continually seeing God for themselves.”

The future tense also convey the idea of certainty. The pure in heart

"shall certainly, continually see God for themselves".

Purity of heart cleanses the eyes of the soul so that God is "visible" (cf John 14:21, see note Hebrews 11:27)

Blest are the pure, whose hearts are clean,
Who never tread the ways of sin;
With endless pleasures they shall see
A God of spotless purity.
---Isaac Watts (Play)

Pritchard writes that there is something in man that wants to see God and so Jesus' words...

touch a nerve deep in the human heart. Jesus here promises that which all men desire—to see God. The Bible tells us that God has put eternity in the heart of every man. Pascal speaks of the “God-shaped vacuum” inside the human heart. Augustine said that our hearts are restless until they find their rest in God. Seeing God is the goal of all religion, the end of all true science, the desire of every nation, and the aim of all philosophy.

(Pritchard goes on to qualify this "sight" noting that...) "You only see what you are looking for. This principle explains so many things that happen to us. A few years ago someone on staff said they were going to walk down to Starbucks to get a cup of coffee. I looked at them and said, “Where is Starbucks?” I had no idea where it was even though it’s only located two blocks from here on Lake Street and I had passed it at least 100 times. But I don’t drink coffee so I have no need to go to Starbucks. Even though I had passed by the store many times, I never saw it. That explains why many of us never “see” God. We aren’t looking for him so we miss him. That, by the way, answers an interesting Bible question. If Jesus really was the Son of God, how could so many people have missed his true identity? The answer is, most people weren’t looking for the Son of God so they never saw him. He lived on this earth for 33 years but most people never knew it. In the spiritual realm, as in all of life, you only see what you are looking for. What We Are Determines What We See. Read Psalm 18:20-26. What we are determines we see! The kind of people we are determines the kind of revelation we receive.

In this context, “seeing God” means to have a deep experience of God, to know him intimately and personally. All successful marriages discover this truth on a human level. The longer you live with another person, the more you get to know them as they really are. Transparency begets intimacy. In a good marriage, there is nothing hidden because there is nothing to hide... Let me summarize this beatitude in a two short statements: 1. In this life a pure heart means a deep walk with God. 2. In eternity a pure heart means a new experience of God. This is what Psalm 24 means when it asks “Who may ascend the hill of the Lord? Who may stand in his holy place?” The answer is simple: “He who has clean hands and a pure heart.” He will receive a blessing from the Lord. He will be vindicated by God himself.

That leads me to one final passage that has always intrigued me. Hebrews 11:27 (note) says (speaking of Moses), “By faith he left Egypt, not fearing the king’s anger; he persevered because he saw him who is invisible.” What an amazing phrase! Moses saw “him who is invisible.” But according to 2 Corinthians 3:11-18 we have an even greater privilege than Moses had. When he saw God the glory eventually faded from his face, but in Christ the veil has been taken away and now in Christ we have seen God face to face and his glory has been revealed to us. More than that, by the Holy Spirit we are daily being transformed into his likeness with “ever-increasing glory.” As I scan this beatitude and think about what it really means, I want to take off my shoes. Surely we are standing on holy ground. . (Pritchard, R: The Tragedy of Double Vision)

We can't physically see God now with our human physical eyes, and so it follows that in this beatitude,  Jesus is speaking figuratively of spiritual vision (and in concert with the meaning of katharos discussed above He is specifically speaking of "20/20 Spiritual Vision"). The Scripture repeatedly states that no human has physically seen God the Father...

"But He (God to Moses) said, "You cannot see My face, for no man can see Me and live!" (Exodus 33:20) (Note: Even Moses who talked with God face to face in Nu 12:8 never God saw in His essence but only saw the “back side” of God. Seeing God’s essence is like looking directly into the sun. The light is too bright, it destroys your eyesight)

"Then the LORD spoke to you from the midst of the fire; you heard the sound of words, but you saw no form-- only a voice." (Deut 4:12)

"And the Father who sent Me, He has borne witness of Me. You have neither heard His voice at any time, nor seen His form." (John 5:37)

"Not that any man has seen the Father, except the One who is from God; He has seen the Father" (John 6:46)

"(God) who alone possesses immortality and dwells in unapproachable light; whom no man has seen or can see. To Him be honor and eternal dominion! Amen." (1Timothy 6:16)

No one has beheld God at any time; if we love one another, God abides in us, and His love is perfected in us. (1John 4:12)

The Scriptures however do state that seeing Jesus was tantamount to seeing the Father.  For example...

"No man has seen God at any time; the only begotten God, who is in the bosom of the Father, He has explained (source of our word exegesis = explanation or critical interpretation of a text) Him. (John 1:18)

"Jesus said to him, "Have I been so long with you, and yet you have not come to know Me, Philip? He who has seen Me has seen the Father; how do you say, 'Show us the Father'?" (John 14:9)

"If I had not done among them the works which no one else did, they would not have sin; but now they have both seen and hated Me and My Father as well. (John 15:24)

"And He (Jesus) is the image of the invisible God, the first-born of all creation. (see note Colossians 1:15)

"And He (Jesus) is the radiance of His (the Father's) glory and the exact representation of His (the Father's) nature, and upholds all things by the word of His power. (see note Hebrews 1:3)

In addition there are numerous Old Testament appearances of God (theophanies) which when carefully observed leave little doubt that the One Who appeared was the Pre-incarnate Christ (Christophanies) in a form usually designated as the "Angel of the Lord". (click study). For example Jacob undoubtedly had a theophany of this type, for Moses records...

So Jacob named the place Peniel, for he said, "I have seen God face to face, yet my life has been preserved." (Genesis 32:30 )

In summary, the seeing that Jesus is referring to in this Beatitude is seeing with the eyes of the heart so to speak. Horao, the root verb of optánomai is used twice in Romans 1:20 (note)