3 C. What do you mean by this perversity, or, rather, senseless contention? Will you not grant me even so much— that when a man leaves the waters of baptism he is free from sin?
A. Either I fail to express my meaning clearly, or you are slow of apprehension.
C. How so?
A. Remember both what you maintained and also what I say. You argued that a man can be free from sin if he chooses. I reply that it is an impossibility; not that we are to think that a man is not free from sin immediately after baptism, but that that time of sinlessness is by no means to be referred to human ability, but to the grace of God. Do not, therefore, claim the power for man, and I will admit the fact. For how can a man be able who is not able of himself? Or what is that sinlessness which is conditioned by the immediate death of the body? Should the man's life be prolonged, he will certainly be liable to sins and to ignorance.
C. Your logic stops my mouth. You do not speak with Christian simplicity, but entangle me in some fine distinctions between being and ability to be.
A. Is it I who play these tricks with words? The article came from your own workshop. For you say, not that a man is free from sin, but that he is able to be; I, on the other hand, will grant what you deny, that a man is free from sin by the grace of God, and yet will maintain that he is not able of himself.
C. It is useless to give commandments if we cannot keep them.
A. No one doubts that God commanded things possible. But because men do not what they might, therefore the whole world is subject to the judgment of God, and needs His mercy. On the other hand, if you can produce a man who has fulfilled the whole law, you will certainly be able to show that there is a man who does not need the mercy of God. For everything which can happen must either take place in the past, the present, or the future. As to your assertion that a man can be without sin if he chooses, show that it has happened in the past, or at all events that it does happen at the present day; the future will reveal itself. If, however, you can point to no one who either is, or has been, altogether free from sin, it remains for us to confine our discussion to the future. Meanwhile, you are vanquished and a captive as regards two out of three periods of time, the past and the present. If anyone hereafter shall be greater than patriarchs, prophets, apostles, inasmuch as he is without sin, then you may perhaps be able to convince future generations as to their time.
Source: Against the Pelagians (New Advent)