On the contrary, Gregory says (Moral. xxxiv, 23) that "pride is a most evident sign of the reprobate, and contrariwise, humility of the elect." But men do not become reprobate on account of venial sins. Therefore pride is not a venial but a mortal sin.
I answer that, Pride is opposed to humility. Now humility properly regards the subjection of man to God, as stated above (Q. 161, A. 1, ad 5). Hence pride properly regards lack of this subjection, in so far as a man raises himself above that which is appointed to him according to the Divine rule or measure, against the saying of the Apostle (2 Cor. 10:13), "But we will not glory beyond our measure; but according to the measure of the rule which God hath measured to us." Wherefore it is written (Ecclus. 10:14): "The beginning of the pride of man is to fall off from God" because, to wit, the root of pride is found to consist in man not being, in some way, subject to God and His rule. Now it is evident that not to be subject to God is of its very nature a mortal sin, for this consists in turning away from God: and consequently pride is, of its genus, a mortal sin. Nevertheless just as in other sins which are mortal by their genus (for instance fornication and adultery) there are certain motions that are venial by reason of their imperfection (through forestalling the judgment of reason, and being without its consent), so too in the matter of pride it happens that certain motions of pride are venial sins, when reason does not consent to them.
Reply Obj. 1: As stated above (A. 2) pride is a general sin, not by its essence but by a kind of influence, in so far as all sins may have their origin in pride. Hence it does not follow that all sins are mortal, but only such as arise from perfect pride, which we have stated to be a mortal sin.
Reply Obj. 2: Pride is always contrary to the love of God, inasmuch as the proud man does not subject himself to the Divine rule as he ought. Sometimes it is also contrary to the love of our neighbor; when, namely, a man sets himself inordinately above his neighbor: and this again is a transgression of the Divine rule, which has established order among men, so that one ought to be subject to another.
Reply Obj. 3: Pride arises from virtue, not as from its direct cause, but as from an accidental cause, in so far as a man makes a virtue an occasion for pride. And nothing prevents one contrary from being the accidental cause of another, as stated in Phys. viii, 1. Hence some are even proud of their humility. _______________________
SIXTH ARTICLE [II-II, Q. 162, Art. 6]
Whether Pride Is the Most Grievous of Sins?
Objection 1: It would seem that pride is not the most grievous of sins. For the more difficult a sin is to avoid, the less grievous it would seem to be. Now pride is most difficult to avoid; for Augustine says in his Rule (Ep. ccxi), "Other sins find their vent in the accomplishment of evil deeds, whereas pride lies in wait for good deeds to destroy them." Therefore pride is not the most grievous of sins.
Obj. 2: Further, "The greater evil is opposed to the greater good," as the Philosopher asserts (Ethic. viii, 10). Now humility to which pride is opposed is not the greatest of virtues, as stated above (Q. 61, A. 5). Therefore the vices that are opposed to greater virtues, such as unbelief, despair, hatred of God, murder, and so forth, are more grievous sins than pride.
Obj. 3: Further, the greater evil is not punished by a lesser evil. But pride is sometimes punished by other sins according to Rom. 1:28, where it is stated that on account of their pride of heart, men of science were delivered "to a reprobate sense, to do those things which are not convenient." Therefore pride is not the most grievous of sins.