Objection 1. It would seem that charity does not increase indefinitely. For every movement is towards some end and term, as stated in Metaph. ii, text. 8,9. But the increase of charity is a movement. Therefore it tends to an end and term. Therefore charity does not increase indefinitely.
Objection 2. Further, no form surpasses the capacity of its subject. But the capacity of the rational creature who is the subject of charity is finite. Therefore charity cannot increase indefinitely.
Objection 3. Further, every finite thing can, by continual increase, attain to the quantity of another finite thing however much greater, unless the amount of its increase be ever less and less. Thus the Philosopher states (Phys. iii, 6) that if we divide a line into an indefinite number of parts, and take these parts away and add them indefinitely to another line, we shall never arrive at any definite quantity resulting from those two lines, viz. the one from which we subtracted and the one to which we added what was subtracted. But this does not occur in the case in point: because there is no need for the second increase of charity to be less than the first, since rather is it probable that it would be equal or greater. As, therefore, the charity of the blessed is something finite, if the charity of the wayfarer can increase indefinitely, it would follow that the charity of the way can equal the charity of heaven; which is absurd. Therefore the wayfarer's charity cannot increase indefinitely.
On the contrary, The Apostle says (Philippians 3:12): "Not as though I had already attained, or were already perfect; but I follow after, if I may, by any means apprehend," on which words a gloss says: "Even if he has made great progress, let none of the faithful say: 'Enough.' For whosoever says this, leaves the road before coming to his destination." Therefore the wayfarer's charity can ever increase more and more.
I answer that, A term to the increase of a form may be fixed in three ways: first by reason of the form itself having a fixed measure, and when this has been reached it is no longer possible to go any further in that form, but if any further advance is made, another form is attained. And example of this is paleness, the bounds of which may, by continual alteration, be passed, either so that whiteness ensues, or so that blackness results. Secondly, on the part of the agent, whose power does not extend to a further increase of the form in its subject. Thirdly, on the part of the subject, which is not capable of ulterior perfection.
Now, in none of these ways, is a limit imposed to the increase of man's charity, while he is in the state of the wayfarer. For charity itself considered as such has no limit to its increase, since it is a participation of the infinite charity which is the Holy Ghost. On like manner the cause of the increase of charity, viz. God, is possessed of infinite power. Furthermore, on the part of its subject, no limit to this increase can be determined, because whenever charity increases, there is a corresponding increased ability to receive a further increase. It is therefore evident that it is not possible to fix any limits to the increase of charity in this life.
Reply to Objection 1. The increase of charity is directed to an end, which is not in this, but in a future life.
Reply to Objection 2. The capacity of the rational creature is increased by charity, because the heart is enlarged thereby, according to 2 Corinthians 6:11: "Our heart is enlarged"; so that it still remains capable of receiving a further increase.
Reply to Objection 3. This argument holds good in those things which have the same kind of quantity, but not in those which have different kinds: thus however much a line may increase it does not reach the quantity of a superficies. Now the quantity of a wayfarer's charity which follows the knowledge of faith is not of the same kind as the quantity of the charity of the blessed, which follows open vision. Hence the argument does not prove.
Source: Summa Theologica (New Advent)