St. Leo on Synergy

Pope St. Leo the Great ca. 400-461

Without the grace of God there can be no obedience on man’s part; nor is man ever abandoned by that Good, without which no good can be done. And if carrying out God’s commands proves difficult or impossible for a man, he has no other course but to return to Him who commands, and who gives His precept so that He may excite desire and provide help, as the Prophet says: “Turn your thoughts to God and He will nourish you.” Or is anyone so insolently proud, is anyone so unscathed, does anyone presume himself so immaculate, that he has no need of any renewal? Such a conviction were utterly erroneous, and that man has grown old in excessive vanity who believes that amid the temptations of this life he has been free of every wound. (Sermons 43.1)