Athanasius of Alexandria : Now the so-called gods of the Greeks, unworthy of the name, are faithful neither in their essence nor in their promises. They do not abide everywhere. The local deities come to nought in the course of time and undergo a natural dissolution.… But the God of all, being one really and indeed and true, is faithful, who is ever the same.… He is ever the same and unchanging, deceiving neither in his essence nor in his promise. As again says the apostle writing to the Thessalonians, "Faithful is he who calls you, who also will do it"; for in doing what he promises, he is faithful to his words. And he thus writes to the Hebrews as to the word's meaning "unchangeable": "If we believe not, yet he abides faithful; he cannot deny himself." — Discourses Against the Arians 2.10 Augustine of Hippo : The only thing the Almighty cannot do is what he does not will, in case anybody should consider it was very rash of me to say that the Almighty "cannot" do something. The blessed apostle said it too, "If we do not believe, he remains faithful, for he cannot deny himself." But it is because he does not wish to that he cannot do it, because he cannot even have the will to. Justice, after all, cannot have the will to do what is unjust, or wisdom will what is foolish, or truth will what is false. — SERMONS 214.4 Augustine of Hippo : God is all-powerful, and, since he is all-powerful, he cannot die, he cannot be deceived, he cannot lie, and, as the apostle says, "he cannot disown himself." Very much he cannot do, yet he is all-powerful. It is because he cannot do these things for the very reason that he is all-powerful. If he could die, he would not be all-powerful. If he could lie, if he could be deceived, if he could deceive, if it were possible for him to do an injustice, he would not be omnipotent. If it were in him to do any of this, such acts would not be worthy of the Almighty. Absolutely omnipotent, our Father cannot sin. — A Sermon to Catechumens on the Creed 1.2 John Chrysostom : What then meaneth, "Can do nothing of Himself"? That He can do nothing in opposition to the Father, nothing alien from, nothing strange to Him, which is especially the assertion of One declaring an Equality and entire agreement. But wherefore said He not, that "He doeth nothing contrary," instead of, "He cannot do"? It was that from this again He might show the invariableness and exactness of the Equality, for the expression imputes not weakness to Him, but even shows His great power; since in another place Paul saith of the Father, "That by two immutable things in which it was impossible for God to lie" (Heb. vi. 18): and again, "If we deny Him - He abideth faithful," for "He cannot deny Himself." (2 Tim. ii. 12, 2 Tim. ii. 13.) And in truth this expression, "impossible," is not declaratory of weakness, but power, power unspeakable. For what He saith is of this kind, that "that Essence admitteth not such things as these." For just as when we also say, "it is impossible for God to do wrong," we do not impute to Him any weakness, but confess in Him an unutterable power; so when He also saith, "I can of Mine own Self do nothing," His meaning is, that "it is impossible, nature admits not, that I should do anything contrary to the Father." — Homily on John 38 John Chrysostom : And to show this, he has added, "If we believe not, He abideth faithful: He cannot deny Himself": that is, if we believe not that He rose again, He is not injured by it. He is faithful and unshaken, whether we say so or not. If then He is not at all injured by our denying Him, it is for nothing else than for our benefit that He desires our confession. For He abideth the same, whether we deny Him or not. He cannot deny Himself, that is, His own Being. We may say that He is not; though such is not the fact. It is not in His nature, it is not possible for Him not to be, that is, to go into nonentity. His subsistence always abides, always is. Let us not therefore be so affected, as if we could gratify or could injure Him. But lest any one should think that Timothy needed this advice... — Homily on 2 Timothy 5 Oecumenius : If we are faithless, he remains faithful. He cannot deny himself. If we are faithless, he remains faithful. If we are faithless concerning that he rose from the dead, or that he is God, he remains faithful, that is, true. For having said that he will rise, and that he is God (for this was signified in many ways), he is faithful. For he rose and he is God. He says that he cannot deny himself, so as not to be God or to have risen. Just as he said: There will be no change because of our denial, but he remains faithful and true concerning himself. And to deny, that is, to lie to himself, he cannot do, in not having risen or not being God. For having promised concerning himself, he cannot lie to himself and fail to fulfill the promises. For neither by believing do we make him not God, nor by being unfaithful do we cast out the divine nature, but both in our believing and in our unbelief he himself is God. Therefore, we who believe reap the benefit. But the "It is not possible," instead of, "It is not permitted." "He remains faithful." Therefore, for our salvation, he demands from us consent to him. For, he says, it is not harmed by our denial. — COMMENTARY ON 2 TIMOTHY Philoxenus of Mabbug : Faith is that which is not a name only, nor is it even voice or speech; but it is that which sheweth itself by the true examination of the soul, and by the sure and certain stability of the thoughts, and it denieth not itself, but in this respect also it is to be compared with God, concerning Whom Paul saith, "He cannot deny Himself." Thus also is it with the faith which denieth not itself, which bringeth not doubt upon itself, upon which no suspicion falleth, and whose power fear reacheth not. Everything that it wisheth, it doeth, and whatsoever it seeketh is given unto it. — 13 Ascetic Discourses, Discourse 2 -- On Faith