From Martin Luther’s Commentary on Galatians, commenting on 3:19:
[T]he Law is not to operate on a person after he has been humbled and frightened by the exposure of his sins and the wrath of God. We must then say to the Law: “Mister Law, lay off him. He has had enough. You scared him good and proper.” Now it is the Gospel’s turn. Now let Christ with His gracious lips talk to him of better things, grace, peace, forgiveness of sins, and eternal life.