Whether unbelief is a sin?

❌ Objection 1 : It would seem that unbelief is not a sin. For every sin is contrary to nature, as Damascene proves (De Fide Orth. ii, 4). Now unbelief seems not to be contrary to nature; for Augustine says (De Praedest. Sanct. v) that "to be capable to having faith, just as to be capable of having charity, is natural to all men; whereas to have faith, even as to have charity, belongs to the grace of the faithful." Therefore not to have faith, which is to be an unbeliever, is not a sin.

❌ Objection 2 : Further, no one sins that which he cannot avoid, since every sin is voluntary. Now it is not in a man's power to avoid unbelief, for he cannot avoid it unless he have faith, because the Apostle says (Rm. 10:14): "How shall they believe in Him, of Whom they have not heard? And how shall they hear without a preacher?" Therefore unbelief does not seem to be a sin.

❌ Objection 3 : Further, as stated above (FS, Question [84], Article [4]), there are seven capital sins, to which all sins are reduced. But unbelief does not seem to be comprised under any of them. Therefore unbelief is not a sin.