Galatians 3:19, 24

Why, then, was the law given? It was given alongside the promise to show people their sins. But the law was designed to last only until the coming of the child who was promised. God gave his law through angels to Moses, who was the mediator between God and the people.

Let me put it another way. The law was our guardian until Christ came; it protected us until we could be made right with God through faith.