Whether unbelief is the greatest of sin?
Objection 1: It would seem that unbelief is not the greatest of sins. For Augustine says (De Bapt. contra Donat. iv, 20): "I should hesitate to decide whether a very wicked Catholic ought to be preferred to a heretic, in whose life one finds nothing reprehensible beyond the fact that he is a heretic." But a heretic is an unbeliever. Therefore we ought not to say absolutely that unbelief is the greatest of sins.
Objection 2: Further, that which diminishes or excuses a sin is not, seemingly, the greatest of sins. Now unbelief excuses or diminishes sin: for the Apostle says (1 Tim. 1:12,13): "I . . . before was a blasphemer, and a persecutor and contumelious; but I obtained . . . mercy . . . because I did it ignorantly in unbelief." Therefore unbelief is not the greatest of sins.
Objection 3: Further, the greater sin deserves the greater punishment, according to Dt. 25:2: "According to the measure of the sin shall the measure also of the stripes be." Now a greater punishment is due to believers than to unbelievers, according to Heb. 10:29: "How much more, do you think, he deserveth worse punishments, who hath trodden under foot the Son of God, and hath esteemed the blood of the testament unclean, by which he was sanctified?" Therefore unbelief is not the greatest of sins.
On the contrary, Augustine, commenting on Jn. 15:22, "If I had not come, and spoken to them, they would not have sin," says (Tract. lxxxix in Joan.): "Under the general name, He refers to a singularly great sin. For this," viz. infidelity, "is the sin to which all others may be traced." Therefore unbelief is the greatest of sins.
I answer that, Every sin consists formally in aversion from God, as stated above (FS, Q 71, A 6; FS, Q 73, A 3). Hence the more a sin severs man from God, the graver it is. Now man is more than ever separated from God by unbelief, because he has not even true knowledge of God: and by false knowledge of God, man does not approach Him, but is severed from Him.
Nor is it possible for one who has a false opinion of God, to know Him in any way at all, because the object of his opinion is not God. Therefore it is clear that the sin of unbelief is greater than any sin that occurs in the perversion of morals. This does not apply to the sins that are opposed to the theological virtues, as we shall stated further on (Q 20, A 3; Q 34, A 2, ad 2; Q 39, A 2, ad 3).
Reply to Objection 1: Nothing hinders a sin that is more grave in its genus from being less grave in respect of some circumstances. Hence Augustine hesitated to decide between a bad Catholic, and a heretic not sinning otherwise, because although the heretic's sin is more grave generically, it can be lessened by a circumstance, and conversely the sin of the Catholic can, by some circumstance, be aggravated.
Reply to Objection 2: Unbelief includes both ignorance, as an accessory thereto, and resistance to matters of faith, and in the latter respect it is a most grave sin. In respect, however, of this ignorance, it has a certain reason for excuse, especially when a man sins not from malice, as was the case with the Apostle.
Reply to Objection 3: An unbeliever is more severely punished for his sin of unbelief than another sinner is for any sin whatever, if we consider the kind of sin. But in the case of another sin, e.g. adultery, committed by a believer, and by an unbeliever, the believer, other things being equal, sins more gravely than the unbeliever, both on account of his knowledge of the truth through faith, and on account of the sacraments of faith with which he has been satiated, and which he insults by committing sin.
II–II · Q. 10, Art. 4: Whether every act of an unbeliever is a sin?
Whether every act of an unbeliever is a sin?
Objection 1: It would seem that each act of an unbeliever is a sin. Because a gloss on Rom. 14:23, "All that is not of faith is sin," says: "The whole life of unbelievers is a sin." Now the life of unbelievers consists of their actions. Therefore every action of an unbeliever is a sin.
Objection 2: Further, faith directs the intention. Now there can be no good save what comes from a right intention. Therefore, among unbelievers, no action can be good.
Objection 3: Further, when that which precedes is corrupted, that which follows is corrupted also. Now an act of faith precedes the acts of all the virtues. Therefore, since there is no act of faith in unbelievers, they can do no good work, but sin in every action of theirs.
On the contrary, It is said of Cornelius, while yet an unbeliever (Acts 10:4, 31), that his alms were acceptable to God. Therefore not every action of an unbeliever is a sin, but some of his actions are good.
I answer that, As stated above (FS, Q 85, AA 2,4) mortal sin takes away sanctifying grace, but does not wholly corrupt the good of nature. Since therefore, unbelief is a mortal sin, unbelievers are without grace indeed, yet some good of nature remains in them. Consequently it is evident that unbelievers cannot do those good works which proceed from grace, viz. meritorious works; yet they can, to a certain extent, do those good works for which the good of nature suffices.
Hence it does not follow that they sin in everything they do; but whenever they do anything out of their unbelief, then they sin. For even as one who has the faith, can commit an actual sin, venial or even mortal, which he does not refer to the end of faith, so too, an unbeliever can do a good deed in a matter which he does not refer to the end of his unbelief.
Reply to Objection 1: The words quoted must be taken to mean either that the life of unbelievers cannot be sinless, since without faith no sin is taken away, or that whatever they do out of unbelief, is a sin. Hence the same authority adds: "Because every one that lives or acts according to his unbelief, sins grievously."
Reply to Objection 2: Faith directs the intention with regard to the supernatural last end: but even the light of natural reason can direct the intention in respect of a connatural good.
Reply to Objection 3: Unbelief does not so wholly destroy natural reason in unbelievers, but that some knowledge of the truth remains in them, whereby they are able to do deeds that are generically good. With regard, however, to Cornelius, it is to be observed that he was not an unbeliever, else his works would not have been acceptable to God, whom none can please without faith. Now he had implicit faith, as the truth of the Gospel was not yet made manifest: hence Peter was sent to him to give him fuller instruction in the faith.