"AND lest men should arrogate to themselves the merit of their own faith at least, not understanding that this too is the gift of God, this same apostle, who says in another place that he had "obtained mercy of the Lord to be faithful," here also adds: "and that not of yourselves; it is the gift of God: not of works, lest any man should boast." And lest it should be thought that good works will be wanting in those who believe, he adds further: "For we are His workmanship, created in Christ Jesus unto good works, which God has before ordained that we should walk in them." We shall be made truly free, then, when God fashions us, that is, forms and creates us anew, not as men— for He has done that already— but as good men, which His grace is now doing, that we may be a new creation in Christ Jesus, according as it is said: "Create in me a clean heart, O God." For God had already created his heart, so far as the physical structure of the human heart is concerned; but the psalmist prays for the renewal of the life which was still lingering in his heart."
~St. Augustine: The Enchiridion (or Handbook on Faith, Hope, and Love), Chap. 31.