Good question! But before I answer it, let’s be clear about what is not new: We do not have a new God. We do not have a new standard of righteousness. We do not have a new way of salvation.
We do not have a new God. This should be so obvious that it need not be mentioned. But I do mention it because many people seem to think that God has changed from the OT to the NT. They think in the OT he was all law, condemnation, and judgment; and that in the NT he is all love and grace and mercy. Not so. We have the same God, who is, on the one hand, both holy and just; and on the other, both gracious and merciful. This hasn’t changed. He eternally is what he is.
We have the same God, and he holds us to the same standard of righteousness, which is revealed in his Law. How could it be otherwise? The Law is a reflection of his own righteousness. How could he ever depart from it? His standard is the same in both Testaments.
Likewise, we have the same way of salvation. In both the OT and NT men are justified as a gift of God’s grace, received on the basis of faith. This hasn’t changed. It wasn’t by a different method in the OT.
When Paul discusses our justification in Romans, what does he say? Does he say, “This is a new doctrine,” “a new way of salvation”? Does he say that in former times men were justified by works, or by their obedience to the Law, but now they are justified by faith as a gift of grace? No, he points to the experience of Abraham, whom Scripture says “believed God and it was counted to him as righteousness” (Rom. 4:3; Gen. 15:6). In other words, Abraham was justified in the same way we are justified. We are justified as a gift of God’s grace, received on the basis of faith. All who have ever been saved have been saved in the same way.
So once again: we have the same God who holds us to the same standard of righteousness and offers us the same way of salvation.
So if none of these things are new, what is new about the NT? Several things.
First, the OT looked forward to a Messiah to come; whereas the NT looks to the Messiah who has come.
Second, the OT anticipated with types and shadows the person and work of the Redeemer; whereas the NT sees those types and shadows fulfilled in Jesus.
Third, in the OT redemption was promised; in the NT redemption is accomplished. Now here I want to be careful here so as not to give a wrong impression. When I say that in the OT redemption was promised, whereas in the NT redemption is accomplished, I don’t mean to suggest that men were not redeemed in the OT. Redemption promised and redemption accomplished has to do with the work of Christ in history. Men were truly redeemed, truly forgiven, born again, justified, filled with the Holy Spirit, etc., in the OT in anticipation of the work that Christ would in time perform through his death and resurrection. God was buying on credit, as it were. When you buy an item on credit, you take possession of the item now with a promise to pay for it in the future. This is how God dealt with the saints in the OT period. He purchased them on credit. He took possession of them, saved them, justified them, redeemed them, with a promise to pay for it in the future. The animal sacrifices in the temple were a token of that future payment. The payment itself was the death of Jesus on the cross.
So, in the OT redemption was promised; in the NT redemption is accomplished.
Another thing that is new in the NT—and this is BIG—is GENTILES. Gentiles as Gentiles are made fellow heirs with the Jews of the promises of God (Eph. 3:1-6). Good thing, too, because I would venture to say that nearly every Christian who is listening to me right now is a Gentile. The message of the NT is that because of Christ and what he has done, you don’t need to become a Jew—that is you don’t have to adopt a distinctively Jewish lifestyle—in order to be incorporated into the people of God. There is much to say about how understanding this serves as the key to understanding Paul, especially his argument in Romans and Galatians.