Objection 1: It would seem that charity cannot increase. For nothing increases save what has quantity. Now quantity is twofold, namely dimensive and virtual. The former does not befit charity which is a spiritual perfection, while virtual quantity regards the objects in respect of which charity does not increase, since the slightest charity loves all that is to be loved out of charity. Therefore charity does not increase.
Obj. 2: Further, that which consists in something extreme receives no increase. But charity consists in something extreme, being the greatest of the virtues, and the supreme love of the greatest good. Therefore charity cannot increase.
Obj. 3: Further, increase is a kind of movement. Therefore wherever there is increase there is movement, and if there be increase of essence there is movement of essence. Now there is no movement of essence save either by corruption or generation. Therefore charity cannot increase essentially, unless it happen to be generated anew or corrupted, which is unreasonable.
On the contrary, Augustine says (Tract. lxxiv in Joan.) [*Cf. Ep. clxxxv.] that "charity merits increase that by increase it may merit perfection."
I answer that, The charity of a wayfarer can increase. For we are called wayfarers by reason of our being on the way to God, Who is the last end of our happiness. In this way we advance as we get nigh to God, Who is approached, "not by steps of the body but by the affections of the soul" [*St. Augustine, Tract. in Joan. xxxii]: and this approach is the result of charity, since it unites man's mind to God. Consequently it is essential to the charity of a wayfarer that it can increase, for if it could not, all further advance along the way would cease. Hence the Apostle calls charity the way, when he says (1 Cor. 12:31): "I show unto you yet a more excellent way."
Reply Obj. 1: Charity is not subject to dimensive, but only to virtual quantity: and the latter depends not only on the number of objects, namely whether they be in greater number or of greater excellence, but also on the intensity of the act, namely whether a thing is loved more, or less; it is in this way that the virtual quantity of charity increases.
Reply Obj. 2: Charity consists in an extreme with regard to its object, in so far as its object is the Supreme Good, and from this it follows that charity is the most excellent of the virtues. Yet not every charity consists in an extreme, as regards the intensity of the act.
Reply Obj. 3: Some have said that charity does not increase in its essence, but only as to its radication in its subject, or according to its fervor.
But these people did not know what they were talking about. For since charity is an accident, its being is to be in something. So that an essential increase of charity means nothing else but that it is yet more in its subject, which implies a greater radication in its subject. Furthermore, charity is essentially a virtue ordained to act, so that an essential increase of charity implies ability to produce an act of more fervent love. Hence charity increases essentially, not by beginning anew, or ceasing to be in its subject, as the objection imagines, but by beginning to be more and more in its subject.