John Chrysostom

Wherefore he nowhere says, 'the richness of the gifts,' but "the riches of their liberality." Now what he says is to this effect; 'their poverty not only was no impediment to their being bountiful, but was even an occasion to them of abounding, just as affliction was of feeling joy. For the poorer they were, the more munificent they were and contributed the more readily.' Wherefore also he admires them exceedingly, for that in the midst of so great poverty they had displayed so great munificence. …

Homily 16 on 2 Corinthians ↗

Theophylact of Ohrid

That is, just as their great affliction produced an abundance of joy, so also their great and extreme poverty not only did not hinder them from giving alms, but even more impelled them "to abound in riches." He did not say, however, in riches of giving, but "of generosity," that is, of a sincere disposition toward liberality. For charity is valued not by the abundance of what is given, but by the disposition of those who give. …

Commentary on 2 Corinthians ↗

Thomas Aquinas

Then when he says, "For they gave according to their means," he explains what he said by commending their generosity as to three things, namely, as to the quantity given, the will to give, and the order of giving. As to the quantity given, it was beyond their power. Hence, he says: truly I abounded in riches, for they gave according to their means, as I can testify, and beyond their means, because they gave so much that they were in need later. …

Commentary on 2 Corinthians ↗