Galatians 3:17-19

Galatians 3:17-19. And this I say, that the covenant, that was confirmed before of God in Christ, the law, which was four hundred and thirty years after, cannot disannul, that it should make the promise of none effect. For if the inheritance be of the law, it is no more of promise: but God gave it to Abraham by promise. Wherefore then serveth the law?

Some might argue that, as the law cannot justify, it is useless, but, on the contrary, it serves a very definite purpose, as Paul goes on to show.