We have heard how the Spirit admonishes the unbelievers who strive to save themselves. This evil is inborn in us, that in times of need we run to all gods except the one God. Therefore God meets us with Scripture, where the contention is that all our toil and merits are cut out by the promises alone apart from the works of the Law, as Paul treats of it so richly in Galatians 3:15ff. There he says that God’s covenant was in force out of pure mercy and promise a long time, 400 years in fact, before the Law. These arguments are unfailing: By grace alone all things come to us who merit nothing. Yet the flesh cannot keep silent in afflictions but always runs back to its own resources, and people look for help to their own prayers and merits. Thus the sophists debated whether the blessed Virgin deserved to become a mother. I say that she was made a mother according to promise before she was born, before she gave any thought to the matter. So here Israel should be plucked out of the Babylonian captivity gratis, at no cost, absolutely free. Therefore the prophet meets this evil especially, since all of us, immersed in trials, forget the promises of God and have recourse to our own resources.
“Lectures on Isaiah: Chapters 40-66” in Works, 17:141–142.