Psalm 1 is a very familiar chapter in the Bible and is frequently sung from psalters and hymnals. It speaks about the man who does not follow the way of sinners but who delights in the Law, or the Word, of God. It tells us that God's way is the way to eternal life, whereas the way of sinners leads to destruction and eternal death -- which is the very crux of the Gospel message. Psalm 1 reads:

1 Blessed [is] the man that walks not in the counsel of the ungodly, nor stands in the way of sinners, nor sits in the seat of the scornful.
2 But his delight [is] in the law of the LORD; and in his law does he meditate day and night.
3 And he shall be like a tree planted by the rivers of water, that brings forth his fruit in his season; his leaf also shall not wither; and whatsoever he does shall prosper.
4 The ungodly [are] not so: but [are] like the chaff which the wind drives away.
5 Therefore the ungodly shall not stand in the judgment, nor sinners in the congregation of the righteous.
6 For the LORD knows the way of the righteous: but the way of the ungodly shall perish.

Keep in mind that Christ Himself is the Way, the Truth and the Life:

Jesus saith unto him, I am the way, the truth, and the life: no man comes unto the Father, but by me. John 14:6

In Matthew 7, Christ speaks of a strait gate and a narrow way that leads to eternal life, versus a wide gate and a broad way that leads to destruction (or eternal death):

Enter ye in at the strait gate: for wide [is] the gate, and broad [is] the way, that leads to destruction, and many there be which go in thereat: Because strait [is] the gate, and narrow [is] the way, which leads unto life, and few there be that find it. Matthew 7:13-14

The word "strait" means narrow (it is not an old-english spelling that means straight). Think of the Strait of Gibralter, for example, which is a narrow passage of water or a channel that separates 2 large bodies of water. It can also mean to be in difficulty, such as one who is in dire straits. However, in this context it mostly refers to a narrow passage or gate (versus a wide gate).

So the strait gate and narrow way that Christ speaks of which leads to eternal life is Himself: He is the Way, the Truth and the Life. He is the Truth of God, the very Word of God personified, in Whom alone is eternal life. And He is thus the Way spoken of in Psalm 1 that leads to life, whereas the way of the sinner in Psalm 1 is the broad way that leads to destruction:

For the LORD knows the way of the righteous: but the way of the ungodly shall perish. Psalm 1:6

Now, in verses 1 and 2 of Psalm 1, we read that the man is blessed, that is, he receives the blessing of God, who does not follow in the sinner's footsteps (or the sinner's way). Rather, his delight is in God's Law:

Blessed [is] the man that walks not in the counsel of the ungodly, nor stands in the way of sinners, nor sits in the seat of the scornful. But his delight [is] in the law of the LORD; and in his law doth he meditate day and night. Psalm 1:1-2

God's Law is, of course, the Word of God. Christ Himself, and the true believers, delight in God's Word, the Bible. And Christ is Himself spoken of as the Word in the flesh:

And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth. John 1:14

Revelation 19
11 And I saw heaven opened, and behold a white horse; and he that sat upon him [was] called Faithful and True, and in righteousness he doth judge and make war.
12 His eyes [were] as a flame of fire, and on his head [were] many crowns; and he had a name written, that no man knew, but he himself.
13 And he [was] clothed with a vesture dipped in blood: and his name is called The Word of God.

So, as the blessed man delights in the law of the Lord and meditates upon it day and night, he is delighting in Christ Himself and meditating upon Christ throughout the Bible.

More than that, the blessed man that Psalm 1 speaks of is first and foremost Christ Himself. He is the One Who is ever sinless, thus He is the One who does not walk in the counsel of the ungodly, Who does not stand in the way of sinners, nor sits in the seat of the scornful. He is the One who delights in God's Law and meditates upon it day and night. And then it is only because of Him that the true believers who are in Him are able to do the same more and more as they live out their lives.

This brings us to verse 3 of Psalm 1, which absolutely points to Christ Himself as the Tree of Life, and secondarily, to the believers who are in Him. We read in verse 3 that the man who delights in the Law of the LORD and meditates upon it day and night is like a living tree by the rivers of water:

And he shall be like a tree planted by the rivers of water, that brings forth his fruit in his season; his leaf also shall not wither; and whatsoever he does shall prosper.

Notice in this verse that this tree is planted by the rivers of water, it brings forth fruit in season, its leaf never withers and whatsoever it does, prospers. We see this same tree mentioned in Revelation 22:1-2 which is by the same river of water, yielding its fruit in season and which leaves are for the healing of the nations:

And he shewed me a pure river of water of life, clear as crystal, proceeding out of the throne of God and of the Lamb. In the midst of the street of it, and on either side of the river, [was there] the tree of life, which bare twelve [manner of] fruits, [and] yielded her fruit every month: and the leaves of the tree [were] for the healing of the nations.

While the language is slightly different, it's clear that God is again speaking of a living tree, a Tree of Life, by a river of water which bears fruits in season and has leaves that prosper for the healing of the nations. And this Tree of Life is Christ with the Gospel.

The river of water that gives life to the tree refers to the Holy Spirit and the Gospel, which bring salvation and eternal life:

He that believes on me, as the scripture has said, out of his belly shall flow rivers of living water. (But this spoke he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet [given]; because that Jesus was not yet glorified.) John 7:38-39

But whosoever drinks of the water that I shall give him shall never thirst; but the water that I shall give him shall be in him a well of water springing up into everlasting life. John 4:14

That this tree of life in Revelation 22 has leaves for the healing of the nations refers to Christ as the great Physician Who heals the sick, that is, to heal sinners of their fatal disease of sin that they might have eternal life:

When Jesus heard [it], he saith unto them, They that are whole have no need of the physician, but they that are sick: I came not to call the righteous, but sinners to repentance. Mark 2:17

Putting all of this together, then, Christ is the Tree of Life Who brings forth fruit. He brings the river of life (the Gospel) that fruit might be borne and that sinners might be healed by the leaves of the tree as it is watered by that river. And, as the believers partake of Christ, they themselves are partakers of this Tree of Life, they themselves are spiritually healed of sin and become more and more like Christ as they delight in God's Word, as they delight in Christ and meditate upon Him day and night in the Bible, and as they, too, bring the Gospel that others might become saved. In that sense Psalm 1 verse 3 identifies with them as they are found in Christ and turning away from their sinful ways unto the Way of Life.

This is seen again in Proverbs 3:13-18 where God says that Wisdom (also referring to Christ, the Word of God, though in this case as a Woman called "Wisdom") is a tree of life for the believers:

Happy [is] the man [that] finds wisdom, and the man [that] gets understanding...She [is] a tree of life to them that lay hold upon her: and happy [is every one] that retains her. Proverbs 3:13,18

The opposite of the believers are those who are unsaved and false prophets. They are like dead trees that have no water, and thus, they produce no fruit or corrupt fruit:

These are spots in your feasts of charity, when they feast with you, feeding themselves without fear: clouds [they are] without water, carried about of winds; trees whose fruit withers, without fruit, twice dead, plucked up by the roots; Jude 12

Even so every good tree brings forth good fruit; but a corrupt tree brings forth evil fruit. A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit. Every tree that brings not forth good fruit is hewn down, and cast into the fire. Wherefore by their fruits you shall know them. Matthew 7:17-19

May it be that the Lord would grant us faith, trust and hope in Him, and a delight in His Word through Christ Jesus.

Blessed [is] the man that trusts in the LORD, and whose hope the LORD is. For he shall be as a tree planted by the waters, and [that] spreads out her roots by the river, and shall not see when heat comes, but her leaf shall be green; and shall not be careful in the year of drought, neither shall cease from yielding fruit. Jeremiah 7:7-8