Now wherever it is said, Do not do this, and Do not do that, and wherever there is any requirement in the divine admonitions for the work of the will to do anything, or to refrain from doing anything, there is at once a sufficient proof of free will. No man, therefore, when he sins, can in his heart blame God for it, but every man must impute the fault to himself. Nor does it detract at all from a man's own will when he performs any act in accordance with God. Indeed, a work is then to be pronounced a good one when a person does it willingly; then, too, may the reward of a good work be hoped for from Him concerning whom it is written, He shall reward every man according to his works. Matthew 16:27
It is, however, to be feared lest all these and similar testimonies of Holy Scripture (and undoubtedly there are a great many of them), in the maintenance of free will, be understood in such a way as to leave no room for God's assistance and grace in leading a godly life and a good conversation, to which the eternal reward is due; and lest poor wretched man, when he leads a good life and performs good works (or rather thinks that he leads a good life and performs good works), should dare to glory in himself and not in the Lord, and to put his hope of righteous living in himself alone; so as to be followed by the prophet Jeremiah's malediction when he says, Cursed is the man who has hope in man, and makes strong the flesh of his arm, and whose heart departs from the Lord. Jeremiah 17:5
Therefore, my dearly beloved, as we have now proved by our former testimonies from Holy Scripture that there is in man a free determination of will for living rightly and acting rightly; so now let us see what are the divine testimonies concerning the grace of God, without which we are not able to do any good thing.
CHURCH FATHERS: On Grace and Free Will (St. Augustine)
It is, however, to be feared lest all these and similar testimonies of Holy Scripture (and undoubtedly there are a great many of them), in the maintenance of free will, be understood in such a way as to leave no room for God's assistance and grace in leading a godly life and a good conversation, to which the eternal reward is due; and lest poor wretched man, when he leads a good life and performs good works (or rather thinks that he leads a good life and performs good works), should dare to glory in himself and not in the Lord, and to put his hope of righteous living in himself alone; so as to be followed by the prophet Jeremiah's malediction when he says, Cursed is the man who has hope in man, and makes strong the flesh of his arm, and whose heart departs from the Lord. Jeremiah 17:5
Therefore, my dearly beloved, as we have now proved by our former testimonies from Holy Scripture that there is in man a free determination of will for living rightly and acting rightly; so now let us see what are the divine testimonies concerning the grace of God, without which we are not able to do any good thing.
CHURCH FATHERS: On Grace and Free Will (St. Augustine)