John Chrysostom

"While they themselves also with supplication." 'For in respect of these things,' saith he, 'they give thanks to God, but in respect of your love and your coming together, they beseech Him that they may be counted worthy to see you. For they long after this, not for the money's sake, but that they may be witnesses of the grace that hath been bestowed upon you.' Seest thou Paul's wisdom, how after having exalted them, he ascribed the whole to God by calling the thing "grace?" For seeing he had spoken great things of them, in that he …

Homily 20 on 2 Corinthians ↗

Theophylact of Ohrid

Moreover, they also pray for you, as though to be counted worthy of seeing you, not for the sake of possessions, but for the sake of the grace of God abundantly given to you. Again he calls the work of almsgiving grace, ascribing everything to God, so that they might not become proud. With the words "the exceeding grace of God" he urges them to make their generosity more abundant, so that others might not surpass and outdo them.

Commentary on 2 Corinthians ↗

Thomas Aquinas

Thirdly, on account of what these saints have from God that they may give thanks to God; hence he says: glorifying God also in their praying for you, i.e., they glorify God for the fact that those holy men pray for you; the men, I say, who are desirous of seeing you in eternal happiness; and this because of the surpassing grace of God in you.

Commentary on 2 Corinthians ↗