10 And herein I give my advice: for this is expedient for you, who have begun before, not only to do, but also to be forward a year ago.
[AD 407] John Chrysostom on 2 Corinthians 8:10
"And herein I give you my advice for your profit."

See how again he is careful to give no offense and softens down what he says, by these two things, by saying, "I give advice," and, "for your profit." 'For, neither do I compel and force you,' says he, 'or demand it from unwilling subjects; nor do I say these things with an eye so much to the receivers benefit as to yours.' Then the instance also which follows is drawn from themselves, and not from others.

"Who were the first to make a beginning a year ago, not only to do, but also to will."

See how he shows both that themselves were willing, and had come to this resolution without persuasion. For since he had borne this witness to the Thessalonians, that "of their own accord with much intreaty," they had prosecuted this giving of alms; he is desirous of showing of these also that this good work is their own. Wherefore he said, "not only to do, but also to will," and not "begun," but "begun before, a year ago." Unto these things therefore I exhort you, whereunto ye beforehand bestirred yourselves with all forwardness.

[AD 458] Theodoret of Cyrus on 2 Corinthians 8:10
Paul knows and respects their willingness to help, but the time has now come for that willingness to be translated into action.