There are many reasons why pastors must preach from the Old Testament:
1. The Old Testament is part of the Christian canon.
2. It discloses the history of redemption leading to Christ.
3. It proclaims truths not found in the New Testament.
4. It helps us understand the New Testament.
5. It prevents misunderstanding of the New Testament.
6. It provides a fuller understanding of Christ.
Sidney Greidanus