Galatians 3:19, 23

Why then was the law given at all? It was given alongside the promise to show people their sins. But the law was designed to last only until the coming of the “Seed,” the child who was promised. When God gave the law, he gave it first to angels; they gave it to Moses, his mediator, who then gave it to the people.

So until the revelation of faith for salvation was released, the law was a jailer, holding us as prisoners under lock and key until the “faith,” which was destined to be revealed, would set us free.