Why are the Old Testament and New Testament so different?

In last week’s sermon text, God killed two newly ordained priests for bringing “unauthorized fire” before Him as an offering (Leviticus 10). It’s a shocking story, and it highlights one of the most stark differences between the worship of God’s people in the Old Testament and the New Testament. All the strict and detailed regulations of the OT seem to give way to tremendous freedom and variation from church to church in the NT. How do we reconcile this difference?

The answer emerges when we take a closer look at exactly what is regulated in each period. In the OT, what was so closely protected were the articles and ceremonies associated with the sacrificial system, the priesthood, and the temple. In the NT, it’s the gospel message of salvation by grace alone through faith alone in Christ alone. In the OT, if you messed with the sacrificial system, you were in deep trouble; in the NT, tampering with the gospel will get you cursed. Paul can abide wrong motives for preaching the gospel (Phil 1:15-18), but he cannot abide preaching the wrong gospel (Gal 1:8).

Why this difference? Actually, there is no difference! Through the worship rituals of the temple and tabernacle, God was proclaiming the message of salvation through Jesus Christ with images and shadows. He wasn’t fussing over some arbitrary rituals; He was guarding the honor of His Son and the salvation to be found in Him alone. The sacrificial system of the OT preached the gospel in symbols, while the NT preaches it in verbal propositions. So in both time periods, what God protects so carefully is the message of the gospel.

This furnishes us with a regulating principle for our worship under the New Covenant: whatever conforms to the gospel is most appropriate. Adoration of God, confession of sin, proclamation of Jesus’ death and resurrection, and expressions of faith and gratitude—these elements all have the shape of the gospel and are thus normal for Christian worship today.

I like to think of it like this: the shape of a container derives from what it holds inside. That’s why egg cartons and milk cartons are shaped the way they are. Likewise with our worship gatherings, which take their shape from the contents they hold—namely, the message of the cross.