Because of what the Bible is Revelation from God. In the Bible God has spoken and through this book God reveals himself, reveals who and what man is, and what his plan for man consists of. The Bible was given to us by God to be read and meditated on. Because of what man is and needs Reconciliation to God and one another. Because man is a holistic being, his spiritual, psychological, and physical faculties are complexly intertwined.
Meditation affects man's whole being.
Another reason is the fact man does not innately contain God's thoughts and ways. Because of what the meditation does Reformation of the mind and life. Many of our problems are symptoms of underlying dynamic mental processes going on inside.