Summary: A classic sermon by St. Augustine.
Chapter 1 [I.]— The Occasion and Argument of This Work.
With reference to those persons who so preach and defend man's free will, as boldly to deny, and endeavour to do away with, the grace of God which calls us to Him, and delivers us from our evil deserts, and by which we obtain the good deserts which lead to everlasting life: we have already said a good deal in discussion, and committed it to writing, so far as the Lord has vouchsafed to enable us. But since there are some persons who so defend God's grace as to deny man's free will, or who suppose that free will is denied when grace is defended, I have determined to write somewhat on this point to your Love, my brother Valentinus, and the rest of you, who are serving God together under the impulse of a mutual love. For it has been told me concerning you, brethren, by some members of your brotherhood who have visited us, and are the bearers of this communication of ours to you, that there are dissensions among you on this subject. This, then, being the case, dearly beloved, that you be not disturbed by the obscurity of this question, I counsel you first to thank God for such things as you understand; but as for all which is beyond the reach of your mind, pray for understanding from the Lord, observing, at the same time peace and love among yourselves; and until He Himself lead you to perceive what at present is beyond your comprehension, walk firmly on the ground of which you are sure. This is the advice of the Apostle Paul, who, after saying that he was not yet perfect, Philippians 3:12 a little later adds, “Let us, therefore, as many as are perfect, be thus minded,” Philippians 3:15 — meaning perfect to a certain extent, but not having attained to a perfection sufficient for us; and then immediately adds, “And if, in any thing, you be otherwise minded, God shall reveal even this unto you. Nevertheless, whereunto we have already attained, let us walk by the same rule.” Philippians 3:16 For by walking in what we have attained, we shall be able to advance to what we have not yet attained—God revealing it to us if in anything we are otherwise minded—provided we do not give up what He has already revealed.
Chapter 2 [II.]— He Proves the Existence of Free Will in Man from the Precepts Addressed to Him by God.
Now He has revealed to us, through His Holy Scriptures, that there is in a man a free choice of will. But how He has revealed this I do not recount in human language, but in divine. There is, to begin with, the fact that God's precepts themselves would be of no use to a man unless he had free choice of will, so that by performing them he might obtain the promised rewards. For they are given that no one might be able to plead the excuse of ignorance, as the Lord says concerning the Jews in the gospel: “If I had not come and spoken unto them, they would not have sin; but now they have no excuse for their sin.” John 15:22 Of what sin does He speak but of that great one which He foreknew, while speaking thus, that they would make their own— that is, the death they were going to inflict upon Him? For they did not have “no sin” before Christ came to them in the flesh. The apostle also says: “The wrath of God is revealed from heaven against all ungodliness and unrighteousness of men who hold back the truth in unrighteousness; because that which may be known of God is manifest in them; for God has showed it unto them. For the invisible things of Him are from the creation of the world clearly seen— being understood by the things that are made— even His eternal power and Godhead, so that they are inexcusable.” Romans 1:18-20 In what sense does he pronounce them to be “inexcusable,” except with reference to such excuse as human pride is apt to allege in such words as, “If I had only known, I would have done it; did I not fail to do it because I was ignorant of it?” or, “I would do it if I knew how; but I do not know, therefore I do not do it”? All such excuse is removed from them when the precept is given them, or the knowledge is made manifest to them how to avoid sin.