God's Demands and Man's Inability

Augustin on God's demands in the face of human inability:

The Pelagians think that they know something great when they assert that "God would not command what He knew could not be done by man." But God commands some things which we cannot do, in order that we many know what we ought to ask of Him [italics mine]. For this is faith itself, which obtains by prayer what the law commands.

 —"On Grace and Free Will," in the Nicene and Post-Nicene Fathers (transl. Peter Holmes and Robert Ernest Wallis; transl. rev. Benjamin B. Warfield; vol. 5, ed. Philip Schaff; Hendrickson: Peabody, 1999), p. 457.