Augustine of Hippo

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.

Now every dispensation of the Old Testament was given through angels, the Holy Spirit working in them and in the very Word of truth, though not yet incarnate, yet never departing from some true ordering of providence. This law was given through angels, sometimes acting in their own person, sometimes in that of God, as was also the way of the prophets.… The children [of Abraham] were put in the hand of [Christ] the Mediator so that he himself might liberate them from sin when they were forced by their transgression of the law to admit that they needed grace and mercy from the Lord.