This image evokes the blessings of the garden of Eden. The garden of Eden was watered by a river which had four headstreams (Genesis 2:9–14). There Adam could flourish in a life with God and be truly blessed. This picture of unlimited fruitfulness is now used in Psalm 1. It is as if delight in the Word of the Lord brings one back into a paradisiacal life; whatever he does prospers.
3 He is like a tree planted by streams of water that yields its fruit in its season, and its leaf does not wither. In all that he does, he prospers.