Augustine of Hippo

Therefore it rests not in human power but on God's, that we have the "power to be made the sons of God." They receive it from him who inspires in the human heart devout thoughts, through which it possesses "faith which works through love." For acquiring and retaining this good, and for progressing perseveringly in it to the end, "We are not sufficient to think anything as of ourselves, but our sufficiency is from God," in whose power are our heart and our thoughts.