Why then the law? It was added because of transgressions, till the descendant should come to whom the promise was made; and it was ordained by angels in the hand of a mediator.
All Commentaries on Galatians 3:19 Go To Galatians 3
Augustine of Hippo
AD 430
Here arises a rather pertinent question: if faith justifies and even the former saints, who were justified before God, were justified through it, what need was there for the law to be given? … The law was given to a proud people, but the grace of love cannot be received by any but the humble. Without this grace the precepts of the law cannot possibly be fulfilled. Israel was rendered humble by transgression, so that it might seek grace and might not arrogantly suppose itself to be saved by its own merits; and so it would be righteous, not in its own power and might but by the hand of the Mediator who justifies the ungodly.