Here are seven reasons why John Piper thinks so.
1. States the cause and result of our broken universe
2. Clearly articulates God's intention for humanity
3. Shows the distinct actions of the persons of the Trinity
4. Shows the depths of our need for God and the height of His grace
5. Opens us to trust the invitations of God
6. Widely and specifically expresses the goodness and trustworthiness of God
7. Shows us glorious truths to help us love God