Psalm 1:3 says the blessed man, who meditates day and night in God's Word will "be like a TREE planted by the RIVERS of WATER that brings forth its fruit in its season, whose leaf also shall not wither; and whatever he does shall prosper." Our ROOT system is our FAITH in God, which connects us to God's life and grace in His Spirit. The secret of a tree’s success is its roots, which are invisible, underground, representing our heart. As we meditate in His Word, our faith-roots becomes stronger, which means that our ability to draw on the waters of the Holy Spirit increases, causing us to thrive, become strong, upright and evergreen, and bear much fruit. That fact that we are planted by the River of Life, means that in Christ, we have continual access to the grace of God in the Holy Spirit. We cannot bear fruit of ourselves - the key is drawing from the life of the River of God. Fruit that glorifies God is produced by the Divine life that flows in and through us (John 15:1-16). We allow God’s life to flow by meditating on God’s Word (to strengthen our faith) and drawing upon His Spirit by faith.
We look at a number of other scriptures that use this same imagery of believers being like fruitful Trees planted by rivers of water (Jeremiah 17:5-8, Isaiah 61:3, 37:31). We see this imagery in the first earthly Temple of the Garden of Eden (Genesis 2-3), and the Millennial Temple, in Ezekiel 47:12: “Along the bank of the river, on this side and that, will grow all kinds of trees used for food; their leaves will not wither, and their fruit will not fail. They will bear fruit every month, because their water flows from the Sanctuary. Their fruit will be for food, and their leaves for medicine.” Also we see it in the everlasting heavenly Temple, the New Jerusalem (Revelation 22:1-3). All of these are pictures of us (redeemed mankind), who are God's ultimate Temples. These gardens with trees planted by the river of life are a picture of garden of our soul. Our thoughts, emotions, convictions and commitments are like trees (Proverbs 3:18). If they are formed and filled by the Word and Spirit of God, they are fresh and fruitful, connecting us to His grace. We relate this to recent discoveries that show that our thoughts are imaged by protein structures in the brain. Whereas God's Word forms healthy tree-like structures, evil thoughts of bitterness and hatred manifest as ugly, twisted protein structures. By meditating in the Word, we can renew our mind, so that it becomes a garden full of fruitful trees, all well-watered by the river of life. Since: "as a man thinks in his heart, so he is" (Proverbs 23:7), it follows that the blessed man who is like a flourishing tree (1:3), is a reflection of the state of his heart (the trees growing in his heart). Likewise, the parable of the sower can in interpreted on both levels, for the seed (which is the word of God) can (1) represent the whole spiritual life of a man, or (2) a particular word of God, which grows by meditation in (hearing) the word (watering with the Word), and brings forth fruit. Thus, the measure of a man is determined by His meditation, and all the trees that he allows to grow in his soul determine the kind of man he becomes, that is, how much he becomes like the blessed, strong and fruitful tree described in Psalm 1:3.