Objection 1. It would seem that charity is infused according to the capacity of our natural gifts. For it is written (Matthew 25:15) that "He gave to every one according to his own virtue [Douay: 'proper ability']." Now, in man, none but natural virtue precedes charity, since there is no virtue without charity, as stated above (Question 23, Article 7). Therefore God infuses charity into man according to the measure of his natural virtue.
Objection 2. Further, among things ordained towards one another, the second is proportionate to the first: thus we find in natural things that the form is proportionate to the matter, and in gratuitous gifts, that glory is proportionate to grace. Now, since charity is a perfection of nature, it is compared to the capacity of nature as second to first. Therefore it seems that charity is infused according to the capacity of nature.
Objection 3. Further, men and angels partake of happiness according to the same measure, since happiness is alike in both, according to Matthew 22:30 and Luke 20:36. Now charity and other gratuitous gifts are bestowed on the angels, according to their natural capacity, as the Master teaches (Sent. ii, D, 3). Therefore the same apparently applies to man.
On the contrary, It is written (John 3:8): "The Spirit breatheth where He will," and (1 Corinthians 12:11): "All these things one and the same Spirit worketh, dividing to every one according as He will." Therefore charity is given, not according to our natural capacity, but according as the Spirit wills to distribute His gifts.
I answer that, The quantity of a thing depends on the proper cause of that thing, since the more universal cause produces a greater effect. Now, since charity surpasses the proportion of human nature, as stated above (Article 2) it depends, not on any natural virtue, but on the sole grace of the Holy Ghost Who infuses charity. Wherefore the quantity of charity depends neither on the condition of nature nor on the capacity of natural virtue, but only on the will of the Holy Ghost Who "divides" His gifts "according as He will." Hence the Apostle says (Ephesians 4:7): "To every one of us is given grace according to the measure of the giving of Christ."
Reply to Objection 1. The virtue in accordance with which God gives His gifts to each one, is a disposition or previous preparation or effort of the one who receives grace. But the Holy Ghost forestalls even this disposition or effort, by moving man's mind either more or less, according as He will. Wherefore the Apostle says (Colossians 1:12): "Who hath made us worthy to be partakers of the lot of the saints in light."
Reply to Objection 2. The form does not surpass the proportion of the matter. On like manner grace and glory are referred to the same genus, for grace is nothing else than a beginning of glory in us. But charity and nature do not belong to the same genus, so that the comparison fails.
Reply to Objection 3. The angel's is an intellectual nature, and it is consistent with his condition that he should be borne wholly whithersoever he is borne, as stated in I, 61, 6. Hence there was a greater effort in the higher angels, both for good in those who persevered, and for evil in those who fell, and consequently those of the higher angels who remained steadfast became better than the others, and those who fell became worse. But man's is a rational nature, with which it is consistent to be sometimes in potentiality and sometimes in act: so that it is not necessarily borne wholly whithersoever it is borne, and where there are greater natural gifts there may be less effort, and vice versa. Thus the comparison fails.
Source: Summa Theologica (New Advent)