Why is the Old Testament so important? Since the New Testament so plainly proclaims the good news of Jesus, and salvation comes through Jesus, then why not simply begin the Bible with the Gospels instead of the Old Testament?
The Bible’s answer centers on two foundational truths: the nature of sin and the holiness of God. These themes run through the heart of the Old Testament, and without a clear understanding of them, we cannot fully grasp the meaning of salvation—or see how the end fits into God’s saving plan.
Just like today, many people during Jesus’ and Paul’s time didn’t understand the cross. Paul says in 1 Corinthians 1:18: “The word of the cross is folly to those who are perishing.” He adds, “We preach Christ crucified, a stumbling block to Jews and folly to Gentiles” (1:23). In other words, the meaning of the cross is not immediately obvious. It requires a God-given framework. The simple fact is that we have no framework or categories for understanding what God did in Jesus to save us and the creation if we don’t first understand sin and holiness.
Paul understood his need for redemption. He understood the depth of his depravity and the holiness of God. This is why he was able to say, “I am not ashamed of the gospel for it is the power of God for salvation to everyone who believes” (Rom. 1:16)? Yes, Paul understood these things through God’s grace and the Spirit’s illumination—but the Spirit always reveals truth through the Scriptures, and those Scriptures are grounded in the Old Testament.
When Peter preaches the first Christian sermon at Pentecost (Acts 2:14–42), he doesn’t begin with his own personal testimony or even Jesus’ own teachings. He begins with the Old Testament. Most of his sermon is drawn from the Hebrew Scriptures, explaining Jesus’ death and resurrection as the fulfillment of God’s promises and prophecies. His audience understood because they knew the Old Testament story—its diagnosis of sin and its anticipation of redemption.
Because of the Old Testament, the first Christians understood that God was good, and just, and powerful to a degree beyond human comprehension. Because of the inability to live up to the commands of the law and the law doing its job as a “tutor” to reveal sin and humanity’s enslavement to the power of sin, they were able to grasp what the cross and the resurrection of Jesus meant for them. It meant that all of those promises for redemption that they read about in the Old Testament had been fulfilled in Jesus of Nazareth.
Just like the first Christians, to grasp the cross, and the entire sweep of Jesus’ work—from incarnation to resurrection to Pentecost—we need the theological and historical foundations the Old Testament provides. Without its testimony to human sin and divine holiness, we cannot even begin to understand the gospel.
Take Romans and Hebrews for example, two of the New Testament’s fullest explanations of the cross. Both depend heavily on Old Testament categories. Paul interprets Jesus’ death in terms of sacrifice, atonement, covenant, and justification—all drawn from his deep knowledge of the Law and the Prophets. The writer of Hebrews, addressing a Jewish audience, shows how Jesus’ redemptive work fulfills the Law, priesthood, and tabernacle.
Consider John the Baptist’s proclamation: “Behold, the Lamb of God, who takes away the sin of the world!” (John 1:29). Without the Old Testament sacrificial system, such a statement would be incomprehensible. These foundational truths are established early in the biblical narrative. In the same way, much of what the New Testament says about the end times—especially in the book of Revelation—remains just as unclear unless we first understand the Old Testament.
The gospel did not appear out of nowhere. It came through the Old Testament story—through the covenant people, the Law and the Prophets, the promises and the sacrificial system. If we want to understand Jesus and his mission—especially as it relates to the end of all things—we must begin where the Bible begins, and that’s in the Old Testament.
