"Moreover, brethren, we make known to you the grace of God which hath been given in the Churches of Macedonia." Having encouraged them with these encomiums, he again tries exhortation. For on this account he mingled these praises with his rebuke, that he might not by proceeding from rebuke to exhortation make what he had to say ill received; but having soothed their ears, might by this means pave the way for his exhortation. For he purposeth to discourse of alms-giving; wherefore also he saith beforehand, "I rejoice that in everything I am of good courage concerning you;" by their past good works, making them the more ready to this duty also. And he said not at once, 'Therefore give alms,' but observe his wisdom, how he draws from a distance and from on high the preparation for his discourse. For he says, "I make known to you the grace of God which hath been given in the Churches of Macedonia." For that they might not be uplifted he calleth what they did "grace;" and whilst relating what others did he worketh greater zeal in them by his encomiums on others. And he mentions together two praises of the Macedonians, or rather three; namely, that they bear trials nobly; and that they know how to pity; and that, though poor, they had displayed profuseness in almsgiving, for their property had been also plundered.
By “the grace of God” Paul means the possession of every good thing. He is not excluding the role of free will by saying this but teaching that every good work is made possible by the help of God.
Not in vain did he bestow so many praises upon them above, but with the purpose of softening them, for he intended to urge them toward love of the poor. Therefore he also said above: "I can rely on you," that is, whatever I say to you, you do. However, he did not say outright: give alms, but, setting before them as an example what others had done, he rouses them also to similar zeal. Note that he calls the disposition toward almsgiving "the grace of God." Through this he both makes his own word beyond reproach and calls the Corinthians to almsgiving as to a gift of God. And he did not say: in this or that city, but praises all of Macedonia, so that they too would all be moved to similar zeal.
[AD 384] Ambrosiaster on 2 Corinthians 8:1