F B Meyer writes...

The rewards of the blessed man - He shall be under Divine culture, planted (Ps 92:13); within reach of perennial supplies, planted by rivers (John 7:37, 38,39); prepared against any demand or emergency - fruit in season; unfading beauty and freshness, a spiritual evergreen; and prosperity even in this world, because his life is ordered by discretion and obedience to Divine principles. Joseph realized this picture (Ge 39:3, 4) (Gems from the Psalms)

Like a tree - The psalmist introduces a simile, a term of comparison, which functions much like an open window, which gives us insight into the meaning of the Word. Remember that these "windows" are not to be abused by a fanciful, even "sanctified" imagination, but are to be interpreted in light of the context. The danger of figures of speech is for us to "run wild" with our interpretations, forgetting that even figures of speech are meant to picture a literal truth.

Guy King...

A tree must have water, and it is fascinating to see how some kinds - the alder, for instance - If planted away from it, will instinctively push out their roots in the direction of the water, however far off, seeming, with their tendrils, to be feeling for it, till they find it. (TO MY SON An Expositional Study of II Timothy by Guy King)

Planted (shathal/satal) means to plant or to transplant. The idea is to plant and cultivate a seed or seedling in the ground so it may grow. The picture of the godly man being transplanted is a fitting image of the New Testament truth of the born-again person. We were dead in our trespasses and sins in IN ADAM and when we were born again by the sanctifying work of the Spirit we were transferred from ("transplanted" if you will from) the kingdom of darkness to the kingdom of light and placed IN CHRIST, rooted and grounded in Him.

Planted also speaks of stability in the storms of life. Ray Pritchard elaborates on this picture asking...

How do you know when a tree has good roots? Answer: When the storms come. All the trees look pretty much alike when the sun is shining or a gentle rain is falling, but let a mighty storm with fierce rain and howling winds pass through. Then the true difference is apparent. The trees with few roots are blown over, but the trees with deep roots are still standing when the storm has passed. So it is for the child of God. You won’t know how good your root system is until the storms of life crash against you. Only then will you discover the strength of your spiritual foundation. The only way to be ready for the storm is to spend time now delighting in God’s Word day by day, meditating on its truth, and building a foundation deep and strong for whatever may come your way.

Parallel Isaiah 61:3b and note how or by whom he is planted and why?

So they will be called oaks of righteousness,
The planting of the LORD, that He may be glorified.

The older I get the more I like God's picture of believers as "trees" Psalm 92 testifying that...

PSALM 92:12-14
The righteous man will flourish like the palm tree,
He will grow like a cedar in Lebanon.
Planted in the house of the LORD,
They will flourish in the courts of our God.
They will still yield fruit in old age;
They shall be full of sap and very green.

Streams of water - The Septuagint translates the phrase by streams of water with the Greek phrase "para tas diexodous ton hudaton".

The Greek lexicon BDAG explains that the specific phrase tas diexodous ton hudaton means...

the point where a stream of water flowing underground suddenly breaks through and flows out freely, a spring

The point is that this is not a stagnant pool but a flowing stream, making the image even more vivid in a land where flowing spring fed streams were sparse. How blessed is this man!

Steven Cole explains that...

The psalmist describes the person who delights in God’s Word as a tree planted by streams of water. This is a tree that has been deliberately cultivated, surrounded by these canals or streams so that its roots have a continual supply of water. It is solid and able to withstand drought or storms. It is fruitful and has continual evidence of life and vitality--its leaves do not wither. He sums it up by applying it: “In whatever he does, he prospers.” There’s a truly happy person: the person God blesses with His prosperity, no matter what circumstances of life he finds himself in.

God is not promising financial prosperity here, but rather, soul-prosperity. The so-called “health and wealth” teaching being promoted by some TV preachers, which claims that God promises financial prosperity, is false. God’s servants may be poor in this world’s goods and afflicted by many trials. But they are rich toward God (Luke 12:21), which is true prosperity. (Ibid)

Wiersbe writes...

A tree is a blessing. It holds soil, provides shade and produces fruit. The godly are like trees, with root systems that go deep into the spiritual resources of God's grace (v. 3). But sadly, many professing Christians are not like trees but are like artificial plants or cut flowers with no roots. They may be beautiful for a while, but soon they die.

A tree needs light, water and roots to live. We all have resources upon which we draw life. The question we need to ask ourselves is, Where are our roots? The person God can bless is planted by the rivers of water. We must be careful not to be like Christians who are dry and withered and depend upon their own resources. They are like tumbleweeds, blown about by any wind of doctrine.

To have the blessings of verse 3, we need to meet the conditions of verses 1 and 2. That is, we must first be separated from the world and saturated with the Word to be situated by the waters.

God desires to bless us, but we need to meet certain conditions to receive His blessings. We bear fruit only when we have roots, and we must draw upon spiritual resources to bring forth fruit in due season. To bear the fruit of the Spirit, we must allow the Spirit to work in us and through us.

In contrast to the believer, the ungodly are not like trees but are like chaff. They have no roots, produce no fruit and are blown about. The ungodly reject the Word of God and will perish without hope Ps 1:6). As Christians we must not reject the ungodly but try to reach them. God blesses us so that we might be a blessing to others. His Spirit helps us bear fruit that can help win the lost.

Are you like a tree or like chaff?

We need God's resources to bear fruit. But where we place our roots is paramount. Only as we grow them deeply into the spiritual resources of God's grace will we produce fruit. Make the Bible your spiritual resource. Delight in it and feed your soul with its truth. God can use you to help win the lost.

In Jeremiah 17 we have a passage that closely parallels Psalm 1...

5 Thus says the LORD, "Cursed is the man who trusts in mankind And makes flesh his strength, And whose heart turns away from the LORD.
6 "For he will be like a bush in the desert And will not see when prosperity comes, But will live in stony wastes in the wilderness, A land of salt without inhabitant.

7 "Blessed is the man who trusts in the LORD and whose trust (or hope) is the LORD.
8 "For he will be like a tree planted by the water, that extends its roots by a stream and will not fear when the heat comes; but its leaves will be green, And it will not be anxious in a year of drought Nor cease to yield fruit.

WHO YIELDS ITS FRUIT IN SEASON AND WHOSE LEAF DOES NOT WHITHER AND IN ALL HE DOES HE PROSPERS: (Ps 92:14; Mt 21:34,41) (Is 27:11; Mt 13:6; 21:19; Jn 15:6, Jude 1:12) (Ps 128:2; 129:8; Ge 39:3,23; Joshua 1:7,8; 1Chr 22:11; 2Ch 31:21; 32:23; Is 3:10)

Yields its fruit in season - The more we converse with the word of God the better furnished we are for every good work. Note again the recurring biblical principle: First the root, then fruit. First the Word with obedience and then the bearing of fruit. The sad truth is that so many Christians are more concerned about the leaves and the fruit at the expense of neglecting the root, but the root are the most important part. Unless Christians spend time daily in the Word, and allow the Spirit to feed them, they will wither and die.

Pritchard notes that...

To speak of “fruit in its season” means that the tree produces fruit that expresses its true inner character. How do you spot an orange tree? By the oranges it produces. And how do you spot an apple tree? Look for the apples. Whatever is on the inside must eventually be seen on the outside. Applied to the spiritual life, this means that when our roots are deep in the Word, we will be given whatever we need, whenever we need it. If we need love, from the Word of God will come the strength to produce the fruit of love. If we need a forgiving spirit, from the Word of God will come the strength to forgive. If we need courage, we will produce the fruit of courage. If we need patience and perseverance, the Word of God will produce it in us. This sort of supernatural life is available to every believer, but it will only be fully realized over time as we continue to walk with the Lord and to delight in his Word. (see also study of the fruit of the Spirit - see notes Galatians 5:16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26 -- see  notes Galatians 5:16;  17;  18;  19;  20;  21;  22;   23;  24;  25;  26)

John Piper explains that...

You will be a fruitful person. O for more fruitful people! You know them. They are refreshing and nourishing to be around. You go away from them fed. You go away strengthened. You go away with your taste for spiritual things awakened. Their mouth is a fountain of life. Their words are healing and convicting and encouraging and deepening and enlightening. Being around them is like a meal. This is the effect of delighting in the Word of God and meditating on it day and night. You will yield fruit in season. (Meditate on the Word of the Lord Day and Night)

Regarding the phrase one whose leaf does not whither Piper says...

The point here is that the hot winds are blowing and the rain is not falling and all the other trees that are not planted by streams are withering and dying, but in spite of all the heat and drought, your leaf remains green, because delighting in the Word of God and meditating on it day and night is like being planted by a stream. The happiness of this person is durable. It is deep. It does not depend on which way the wind is blowing or whether the rain is falling. It gets its life from an absolutely changeless source: God in his Word.

Pritchard adds that...

The phrase pictures a leafy tree that seems like an evergreen because its leaves are in season all year round. People like this are constantly refreshed by the Word of God, constantly renewed, constantly drawing on new strength for new situations. They are never boring, never dull, never living off yesterday’s blessings, but living each day in the strength of the Lord whose mercies are new every morning.

Habakkuk describes such a person...

Though the fig tree do not blossom, nor fruit be on the vines, the produce of the olive fail and the fields yield no food, the flock be cut off from the fold and there be no herd in the stalls, yet I will exult in the LORD, I will rejoice in the God of my salvation. (Habakkuk 3:17-18)

Piper says the phrase "he prospers" describes...

a life whose "labor is not in vain" (1 Corinthians 15:58), but succeeds in God's good purposes into eternity. 

Pritchard adds that...

They prosper in the sense that no matter what happens, they find strength for the day and hope in the midst of the hardest difficulties. They bring forth godly fruit in good times and bad times. Why? Because they are planted deep in the good soil and their roots reach out to the water of the Word of God. Finding constant nourishment therein, they can face whatever life throws at them.

The thought here is similar to Romans 8:37  (note) where in the midst of struggles, sorrow, persecution, famine, distress, nakedness and the sword, those who know Jesus are “more than conquerors” through His divine power. And that triumphant deliverance comes to us in large part through the Word of God.

In this world we may face disappointment, sorrow, rejection, failure, sickness, abandonment, and discouragement. We may hear things about our children we prayed to God never to hear, our dearest friends may desert us, our spouse may leave us, and we may face an unremitting series of earthly tragedies. Illness, physical weakness, and death itself may visit our door time and again.

Even then, we prosper, we thrive, we survive, we are not destroyed. Sometimes when I ask friends going through hard times how they are doing, the answer comes back, “I’m surviving.” Years ago I foolishly thought that was a wimpy response. Now I see that it is a powerful statement of faith. Sometimes surviving is the same as thriving. Some days to survive is to prosper. That, too, is a kind of prosperity for the people of God.

Application Questions:

Have you discovered the secret of blessed? Do you really desire to be blessed? Do you understand that although blessed is a supernatural condition, you as a believer still have some responsibility -- there are certain negative behaviors that will impede the flow of God's blessing.

Who are you getting your primary counsel from? If you are not delighting in the God's Word, is it because you are "stuck" in verse 1?