John Chrysostom

What he says is this; 'in the first place ye not only supply the wants of the saints, but ye are abundant even;' that is, 'ye furnish them with even more than they need: next, through them ye send up thanksgiving to God, for they glorify Him for the obedience of your confession.' For that he may not represent them as giving thanks on this account solely, (I mean, because they received somewhat,) see how high-minded he makes them, exactly as he himself says to the Philippians, "Not that I desire a gift." (Philippians chapter 4, verse …

Homily 20 on 2 Corinthians ↗

Theophylact of Ohrid

"The ministration of this service," he says, that is, assistance with possessions, accomplishes much, for it not only supplies the need of the brethren, but also "abounds," that is, provides them more than what is needed; and this service and testimony of the ministry of love for mankind calls forth many thanksgivings.

Commentary on 2 Corinthians ↗

Cyprian

And again: "The administration of this service shall not only supply the wants of the saints, but shall be abundant also by many thanksgivings unto God; ". Also in the same place: "The administration of this service has not only supplied that which is lacking to the saints, but has abounded by much giving of thanks unto God."

Treatise VIII On Works and Alms ↗

Thomas Aquinas

Then when he says, for the rendering of this service, he explains the reason mentioned above, namely, how their abundance works thanksgiving to God. First he shows this; secondly, the reason for thanks (v. 13); thirdly, he breaks out in thanksgiving (v. 14). He says therefore: I say that your abundance works thanksgiving to God, for the rendering of this service of yours, by which you help the saints, has many good results: "As a matter of equality your abundance at the present time should supply their want" (2 Cor. 8:14). …

Commentary on 2 Corinthians ↗