Greek: di' ou kai sozesthe, (2PPPI) tini logo eueggelisamen (1SAMI) humin ei katexete, (2PPAI) ektos ei me eike episteusate. (2PAAI)
Amplified: And by which you are saved, if you hold fast and keep firmly what I preached to you, unless you believed at first without effect and all for nothing. (Amplified Bible - Lockman)
Barclay: and through which you are saved. I want to make clear to you what account I gave you of the good news, an account which can save you if you hold fast to it, unless your belief is a random and haphazard thing. (Westminster Press)

By which also you are saved - This is more literally

through which also you are being saved

Ray Stedman commenting on this subtle difference (are saved versus being saved) writing that...

Paul goes on to say that the gospel is doing a second thing -- by which you are being saved. Now he puts it in the present tense; that is why I translated it that way. It is not by which you "were" saved. That is past tense; or by which you "will be" saved, that is future. It is by which you are now "being" saved. The present tense indicates that he is thinking here about our present, earthly experience of life.

There are three tenses of salvation simply because there are three parts of our human being, our human nature... Now, when you came to Christ that spirit was regenerated; it was made alive; it was indwelt by the Holy Spirit; it was linked to Jesus Himself so that you and He are one Spirit. That is salvation past; that is the past tense, by which you "were" saved, as certain texts say.

Then there is the one in the future: you will be saved. Paul will be talking about these bodies; this is the theme of this great resurrection chapter. This body too has a part in God's plan. God is not going to throw it away. I do not care if you grind it up and burn it up and scatter it to the winds, God can gather it together. We are going to see how, and why, he does it in this very chapter. God has a purpose for your body. He is going to redeem it, and restore it, and it will be useful to you all throughout eternity. That is salvation to come.

But now Paul is talking about the soul, about your life, about how you are living from day to day. He says that is "being" saved according to how much you are resting on God at work in you, and allowing yourself to be the instrument of his grace. In these terms, what he is talking about is buying you back from wasting your life. In these terms, he is telling us that as we walk with him what we do becomes eternally profitable, not only profitable for this present time, but eternally so, so that you can use your money for eternal profit, you can use your time for eternal profit, you can lay up treasures in heaven and not upon earth. By the way you use your moments and your days, whether you employ them in the strength of God or from the energy of the flesh, you can determine what is going to be good and bad at the judgment seat of Christ, when "every one may receive the things done in his body, whether it be good or bad," {cf, 2Cor 5:10}.

Now that is what the gospel is for. The gospel is to give us stability, to give us steadiness, to give us an immovable foundation, to give us a place of recovery, to give us a place of healing and of wholeness, and finally to redeem our present existence so that it has eternal meaning as we live day by day. What a tremendous theme that is! What a marvelous thing that God has prepared for us, in this solid place to stand!

Christ died for our sins according to the Scripture. He was buried. He rose again from the dead according to the Scripture, that we too might learn to die to our sins, to bury them, and to rise again to the freshness and newness of life that we experience right now by faith in Jesus Christ.

Prayer - Heavenly Father, thank you for the marvel, the wonder of the gospel. Help us to understand that this is to be the center of our life, the most basic thing about us is our faith in this good news. Nothing can be more foundational than that. Grant to us Lord, to take it seriously, to know that this is the beginning of a new life as we stand again and again at the place where the gospel brings us. We ask in Jesus' name, Amen. (1Corinthians 15:1-4 Of First Importance)

Saved (4982) (sozo) conveys the basic meaning of rescuing one from great peril. Additional nuances include to protect, keep alive, preserve life, deliver, heal, be made whole.

Sozo is in the present tense (not past tense) which more literally can be translated not as "you have been saved" but  you are being saved. Note the passive voice which indicates it is God Who does the saving. See the related study of the Three Tenses of Salvation to help understand the multi-facet diamond of God's wondrous salvation.  Here Paul is saying in essence that salvation is a continual progression toward Christlikeness. Justification (declaration of righteous standing before God) by faith (past tense salvation) is a once for all transaction in the past, but it initiates a process referred to as sanctification (present tense salvation, cf 1Cor 1:18, 2Cor 2:15, 1 Peter 3:21) which continues (just as we began -- "by grace through faith", a gift from God, thus indicating the necessity of the believer's continual dependence upon the sanctifying power of the Holy Spirit) throughout our earthly life to one day be consummated in the glorification of our bodies (future tense salvation), when faith and hope become sight. In the meantime we are as Paul states in this verse "continually being saved"! Praise God for so great a salvation, which provides for us from the inception to the consummation and then throughout eternity!

Barclay, commenting on the present tense aspect of our salvation, writes that...

Salvation goes from glory to glory. It is not something which is ever completed in this world. There are many things in this life which we can exhaust, but the meaning of salvation is something which a man can never exhaust. (Barclay, W: The Daily Study Bible Series. The Westminster Press or Logos)

More often and here in 1Corinthians 15, sozo refers to salvation in a spiritual sense, a meaning which is illustrated in the following passage where Matthew records the angel's conversation with Joseph declaring

And you will be hated by all on account of My name, but it is the one who has endured to the end who will be saved (sozo). (Mt 10:22, cf Mt 24:13)

IF YOU HOLD FAST THE WORD WHICH I PREACHED TO YOU: tini logo eueggelisamen (1SAMI) humin ei katexete, (2PPAI): (11,12; Proverbs 3:1; 4:13; 6:20-23; 23:23; Colossians 1:23; 2 Thessalonians 2:15; Hebrews 2:1; Hebrews 3:6,14; 4:14; 10:23)

If (1487) (ei) is a condition of first class. Paul assumes that they are holding it fast. In this case ei is used with the indicative mood, implying a possibility without the expression of uncertainty, a condition or contingency as to which there is no doubt.

John MacArthur observes that the if...

does not imply that the believers are in danger of losing their salvation, but it is a warning against non–saving faith. So a clearer rendering would be, “… if you hold fast what I preached to you, unless your faith is worthless or unless you believed without effect.” The Corinthians’ holding fast to what Paul had preached was the result of and an evidence of their genuine salvation, just as their salvation and new life were an evidence of the power of Christ’s resurrection. (MacArthur, J: 1Corinthians. Chicago: Moody Press or Logos)

If you hold fast the word - Charles Hodge explains that hold fast..

does not mean, "if you keep in mind." It simply means, "if you hold fast." Whether that is physically holding on or retaining in the memory or retaining in faith depends on the context. Here it is evident that the condition of salvation is not keeping in mind, but persevering in the faith. "The Gospel saves you," says the apostle, "if you hold firmly to the Gospel that I preached to you." (Hodge, C. 1 Corinthians)

Utley has an interesting note observing that “if”...

is a first class conditional sentence, which implies that they would hold fast to the truth of the gospel, which he preached to them, but it adds a note of contingency by a second ei (unless). This seems to parallel Jesus’ Parable of the Soils (cf. Matt. 13) and John’s discussion in 1John 2:19 of those who were in the fellowship, but left. There were those factions in Corinth who by their actions, attitudes, and theology showed they were never believers! They rejected Paul’s gospel and Apostolic authority and merged the gospel into Roman culture, whereby the culture became dominant! Cultural Christianity is always weak and sometimes not Christian! However, please note that contextually Paul is asserting his confidence that the Corinthian believers are true believers. (1) aorist tense, 1Cor 15:1, received (2). perfect tense, 1Cor 15:1, in which also you stand (3) first class conditional sentence, 1Cor 15:2, “since you hold fast”. (Utley, R. J. D.  Volume 6: Paul's Letters to a Troubled Church: I and II Corinthians. Study Guide Commentary Series. Marshall, Texas: Bible Lessons International)

Hold fast (2722) (katecho from katá = intensifies meaning + écho = have, hold) means to retain whether by avoiding the relinquishing of something. It was used literally of holding one to keep them from going (as in Luke 4:42).

Katecho was used figuratively with the idea of restraining or keeping someone (Antichrist) from exercising power (see 2Thes 2:6-7). A closely related figurative use of katecho means to hold down or suppress as the ungodly do to the truth about God (see note Romans 1:18).

One NT use of katecho means to take over or occupy, to have a place as one’s own or to take into one’s possession.  (see Lu 14:9).

In the passive sense, katecho describes one as being bound by the law (see note Romans 7:6)

Katecho as used here in 1Corinthians 15:2 (see discussion below re Hebrews 3:6, 14) means to adhere firmly to traditions, convictions, or beliefs. Note that our salvation is kept by Christ’s holding us fast, not primarily by our holding Him fast. Our holding onto Him is evidence that He is holding onto us.

Jesus used katecho with a this same meaning in the gospel of Luke declaring...

Luke 8:15 And the seed in the good soil, these are the ones who have heard the word in an honest and good heart, and hold it fast (present tense - refers to their continual attitude toward the word), and bear fruit  (present tense - refers to their continual productivity) with perseverance (see study of hupomone). (Comment: The seed is the Word of God as revealed in the Gospel of Jesus Christ. They not only received this precious word but they allowed the word of God to perform its word in those who believed and were thereby molded into conformity with the image of Christ. They were teachable and obedient, developing true Christian character and producing genuine fruit of good works for the glory of their Father. Their spiritual fruit is clear evidence of their spiritual life. In short, this group manifested evidence of authentic salvation. J Vernon McGee writes "These are the hearers who are genuinely converted by the Word of God." In this parable of the soils, Jesus point was that His disciples would sow much seed, but that they should not be distressed by seemingly poor results including cases of apparent salvation which were in reality nothing but an outward emotional experience as evidenced by the fact that they did not hold fast the word and bear fruit.)

Katecho is used 17 times in the NT (including Lu 8:15)...

Luke 4:42 And when day came, He departed and went to a lonely place; and the multitudes were searching for Him, and came to Him, and tried to keep Him from going away from them.

Luke 14:9 and he who invited you both shall come and say to you, 'Give place to this man,' and then in disgrace you proceed to occupy the last place.

Acts 27:40 And casting off the anchors, they left them in the sea while at the same time they were loosening the ropes of the rudders, and hoisting the foresail to the wind, they were heading for the beach.

Romans 1:18 (note)  For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who suppress the truth in unrighteousness,

Romans 7:6 (note) But now we have been released from the Law, having died to that by which we were bound, so that we serve in newness of the Spirit and not in oldness of the letter.

1 Corinthians 7:30 and those who weep, as though they did not weep; and those who rejoice, as though they did not rejoice; and those who buy, as though they did not possess;

1 Corinthians 11:2 Now I praise you because you remember me in everything, and hold firmly to the traditions, just as I delivered them to you.

1 Corinthians 15:2 by which also you are saved, if you hold fast the word which I preached to you, unless you believed in vain.

2 Corinthians 6:10 as sorrowful yet always rejoicing, as poor yet making many rich, as having nothing yet possessing all things.

1Thessalonians 5:21 (note) But examine everything carefully; hold fast (present imperative) to that which is good;

2 Thessalonians 2:6 And you know what restrains him now, so that in his time he may be revealed.

2 Thessalonians 2:7 For the mystery of lawlessness is already at work; only he who now restrains will do so until he is taken out of the way.

Philemon 1:13 whom I wished to keep with me, that in your behalf he might minister to me in my imprisonment for the gospel;

Hebrews 3:6 (note) but Christ was faithful as a Son over His house whose house we are, if (f indeed, if only, on condition that) we hold fast (First plural singular, aorist, active, subjunctive) our confidence and the boast of our hope firm until the end.

Hebrews 3:14 (note) For we have become partakers of Christ, if we hold fast (First plural singular, aorist, active, subjunctive) the beginning of our assurance firm until the end;

Hebrews 10:23 (note) Let us hold fast (present tense) the confession of our hope without wavering, for He who promised is faithful

Katecho gives a beautiful picture from its use by Luke who invokes katecho as a nautical term meaning to steer toward or land at writing...

Barclay commenting on hold fast writes that the gospel is...

something to which a man has to hold tenaciously. Life makes many an attempt to take away our faith. Things happen to us and to others which baffle our understanding; life has its problems to which there seems no solution and its questions to which there seems no answer; life has its dark places where there seems to be nothing to do but hold on. Faith is always a victory, the victory of the soul which tenaciously maintains its clutch on God. (Barclay, W: The Daily Study Bible Series. The Westminster Press or Logos) (Comment: John writes "For whatever is born of God overcomes the world; and this is the victory that has overcome the world-- our faith." 1John 5:4)

The writer of Hebrews agrees writing that...

Christ was faithful as a Son over His house whose house we are, if we hold fast (katecho - present tense = speaks of our habitual practice) our confidence and the boast of our hope firm until the end. (see note Hebrews 3:6)

Comment: "If" (in contrast to the if in 1Cor 15:2) in Hebrews 3:6 is a third class conditional statement which reflects uncertainty or doubt. In other words a person proves they are truly God's "house" if they do not desert He Who Alone is the Way, the Truth and the Life. Although there are some who do not believe in the perseverance of the saints, verses such as Hebrews 3:6 clearly teach that steadfast faith marks the elect of God and that persistence and hope characterize the genuine members of God's family. One of the greatest of all American theologians, Jonathan Edwards, once said that the sure proof of election is that one holds out to the end. We can tell if we are really the house of God because we stay there. The one who falls away never belonged in the first place. He is not saying you "become the house of God by holding fast" but if you are the house of God you will hold fast. If you do not hold fast you are not the house of God! He is telling us the end result of our salvation...perseverance to the end. FF Bruce writes "Nowhere in the New Testament more than here do we find such repeated insistence on the fact that continuance in the Christian life is the test of reality.

Remember that we can neither save ourselves nor keep ourselves saved. In the present verse, the meaning of hold fast is simply that continuance is the proof of reality.  This is John's point in his first epistle where he writes that...

C H Spurgeon in his sermon Enduring to the End on (Matthew 10:22) writes that...

The Word (3056) (logos from légō = to speak intelligently; English = logic, logical) means something said and describes a communication whereby the mind finds expression in words.

Lógos is a general term for speaking, but always used for speaking with rational content. Lógos is a word uttered by the human voice which embodies an underlying concept or idea. When one has spoken the sum total of their thoughts concerning something, they have given to their hearer a total concept of that thing. Thus the word lógos conveys the idea of “a total concept” of anything. Lógos means the word or outward form by which the inward thought is expressed and made known. Note that lógos does not refer so much just to a part of speech but to a concept or idea. In other words, in classical Greek, lógos never meant just a word in the grammatical sense as the mere name of a thing, but rather the thing referred to, the material, not the formal part. In fact, the Greek language has 3 other words (rhema, onoma, epos) which designate a word in its grammatical sense.

Logos then is translated in with a number of English words (saying, instruction, message, news, preaching, question, statement, teaching, etc)  depending on the context, which in this case is clearly the Gospel.

I preached (2097) (euaggelizo/euangelizo euaggelizo/euangelizo from eu = good, well + aggéllo = proclaim, tell; English = evangelize) means to announce good news concerning something. Euaggelizo was often used in the Septuagint for preaching a glad or joyful message (cf. 1Sam. 31:9; 2 Sa 1:20; 4:10).

Euaggelizo/euangelizo in its original sense could be used to refer to a declaration of any kind of good news, but in the NT it (with 2 exceptions discussed below) refers especially to the glad tidings of the coming kingdom of God and of salvation obtained through Jesus Christ's death, burial and resurrection. Most of NT uses of euaggelizo are translated "preach" or "preach the gospel," whichever fits more smoothly into the context. There are two passages that illustrate the original meaning of simply to "bring glad tidings" or "bring good news" of any nature. The first is in Luke...

Lu 1:19 And the angel answered and said to him (Zacharias), "I am Gabriel, who stands in the presence of God; and I have been sent to speak to you, and to bring you this good news. (that he would have a son, John the Baptist).

The other is 1 Thessalonians...

1Thessalonians 3:6