Blessed is the man who does not walk in the counsel of the wicked or stand in the way of sinners or sit in the seat of mockers. But his delight is in the law of the LORD, and on his law he meditates day and night. He is like a tree planted by streams of water, which yields its fruit in season and whose leaf does not wither. Whatever he does prospers.
Why is the blessed man compared to that of a productive tree planted by streams of water? The blessed man's delight was in the Law of the LORD or Word of God and the frequency by which he meditated on it was at least twice a day - day and night - if not all throughout the day. For just as the man received his spiritual nourishment from consistently being in or delighting himself in God's Word, so the tree draws from the nutrients of the stream of water and produces its fruit in season.
Allow me to work backwards. Do you wish to be productive and yield fruit in season? Then make sure you are planted or Committed to a local body of believers where you can be fed a steady stream of the Word of God. Are you looking to be planted somewhere by The Planter? Stay in God's Word, delight in Him and He will give you the desires of your heart (Psalm 37:4).
The more our roots reach deeper into His Living Water, the more we can grow strong for the winds of life and fruitful for the people in our life. And now, just as you accepted Christ Jesus as your Lord, you must continue to live in obedience to him. Let your roots grow down into him and draw up nourishment from him, so you will grow in faith, strong and vigorous in the truth you were taught. Let your lives overflow with thanksgiving for all he has done. (Colossians 2:6-7) (New Living Version)
The last sentence in the main Scripture above (Psalm 1:1-3) says, "Whatever he does prospers." It is obviously conditional on everything listed before it, but it holds great hope for the one who walks that lifestyle. I hear a similar charge in the New Testament when Jesus said, My true disciples produce much fruit. This brings great glory to my Father. (John 15:8) It is a wonderful thing to be at a place in life where you can bless others and bless God. It is also great to know that because of my delight in His Word and meditation on it day and night He chooses me and appoints me to bear much fruit - the kind that endures (John 15:16).