We read yesterday how King David immersed himself in the Word of God. When I was a child, I remember reading my Bible, and all I had when I was very young was just the New Testament. We were told a few of the stories from the Old Testament, but no one actually read the whole book. Obviously, all that King David had was the Old Testament—the Law and the Prophets and some of the writings of the Prophets who came before him. He did not have the Proverbs, but he taught them to his son Solomon, who later wrote them down. So David did not have as much as you and I have.
However, it is not about memorizing Scripture simply to repeat the words or to show other people that you can memorize it. Memorization is not even required; the Bible does not say anything about Jesus memorizing it, or that they sat and quoted long memorizations of Scripture. No, Jesus followed the Spirit of God and lived it out—that is what he was known for.
What did David do? He put Scripture to song so that he could remember, and he wrote down his own experiences. He put his poetry to music or had a music director put it to music, and they sang it. Merely reading those words does not make you righteous. You could be a young person and not even know how to read and still be like Christ. So it is not about just reading or memorizing; rather, it is letting these words hit your heart so that you change, and it is about letting the Holy Spirit teach you and guide you.
For more on this topic, read History of the One True God – Volume III God-Fearing Families