Nicene and Post-Nicene Fathers, Vol. V:
A Treatise on the Soul and its Origin.: Chapter 11

Chapter 11.—The Apostle Peter Told No Lie, When He Said He Was Ready to Lay Down His Life for the Lord, But Only Was Ignorant of His Will.

But perhaps you despise me for confessing all this, and will in consequence compare me with “cattle.” For myself, however, I will not cease to advise you, or (if you refuse to listen to me) at all events to warn you, to acknowledge rather this common infirmity, in which virtue is perfected; lest, by assuming unknown things to be known, you fail to attain to the truth. For I suppose that there is something which even you wish to understand, but are unable; which you would never seek to understand, unless you hoped some day to succeed in your research. Thus you also are ignorant of the powers of your own understanding, who profess to know all about your own nature, and decline to follow me in my confession of ignorance. Well, there is also the will; what am I to say about that, where certainly free choice is ostentatiously claimed by us? The blessed Apostle Peter, indeed, was willing to lay down his life for the Lord. He was no doubt sincere in his willingness; nor was he treacherous to the Lord when he made the promise. But his will was entirely ignorant of its own powers. Therefore the great apostle, who had discovered his Master to be the Son of God, was unknown to himself. Thus we are quite aware respecting ourselves that we will a thing, or “nill” it; but although our will is a good one, we are ignorant, my dear son, unless we deceive ourselves, of its strength, of its rep. 359 sources, of what temptations it may yield to, or of what it may resist.