Although the Macedonians were short of material resources, their souls were rich, because they ministered to the saints with a pure conscience, trying to please God rather than men.
The affliction of the Macedonians did not lead only to sorrow but also to great rejoicing and generosity. Paul said this in order to prepare the Corinthians to be noble and firm in their sufferings. For they were not merely to be afflicted, they were to use their afflictions as a means of growing in joy.
"How that in much proof of affliction the abundance of their joy."
Do you see his wisdom? For he says not first, that which he wishes; but another thing before it, that he may not seem to do this of set purpose , but to arrive at it by a different connection. "In much proof of affliction." This was what he said in his Epistle to the Macedonians themselves, "You became imitators of the Lord, having received the word in much affliction, with joy of the Holy Ghost;" and again, "From you sounded forth the word of the Lord, not only in Macedonia and Achaia, but also in every place, your faith to God-ward is gone forth." [1 Thessalonians 1:6-8] But what is, "in much proof of affliction the abundance of their joy?" Both, he says, happened to them in excess; both the affliction and the joy. Wherefore also the strangeness was great that so great an excess of pleasure sprang up to them out of affliction. For in truth the affliction not only was not the parent of grief, but it even became unto them an occasion of gladness; and this too, though it was "great." Now this he said, to prepare them to be noble and firm in their trials. For they were not merely afflicted, but so as also to have become approved by their patience: yea rather, he says not by their patience, but what was more than patience, "joy." And neither said he "joy" simply, but "abundance of joy," for it sprang up in them, great and unspeakable.
"And their deep poverty abounded unto the riches of their liberality."
Again, both these with excessiveness. For as their great affliction gave birth to great joy, yea, "abundance of joy," so their great poverty gave birth to great riches of alms. For this he showed, saying, "abounded unto the riches of their liberality." For munificence is determined not by the measure of what is given, but by the mind of those that bestow it.
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. For "their deep," that is, 'their great and unspeakable,' "poverty," showed their "liberality." But he said not 'showed,' but "abounded;" and he said not "liberality," but "riches of liberality;" that is, an equipoise to the greatness of their poverty, or rather much outweighing it, was the bountifulness they displayed.
[AD 384] Ambrosiaster on 2 Corinthians 8:2