John Calvin Commentary 2 Corinthians 8:18

"And we have sent together with him the brother whose praise in the gospel [is spread] through all the churches;" — 2 Corinthians 8:18 (ASV)

We have sent with him the brother. The fact that three persons are sent is evidence that great expectations were held for the Corinthians, and it was important for them to be all the more attentive to duty, so that they would not disappoint the hopes of the Churches. It is uncertain, however, who this second person was; some conjecture that it was Luke, others that it was Barnabas. Chrysostom prefers to consider it to have been Barnabas. I agree with him, because it appears that by the approval of the Churches, he was associated with Paul as a companion. However, since it is almost universally agreed that Luke was one of those who bore this Epistle, I have no objection to his being considered the third one mentioned.

The Apostle honors the second person, whoever he may be, with a significant commendation: that he had conducted himself concerning the gospel in a praiseworthy manner; that is, he had earned praise by promoting the gospel. For, although Barnabas deferred to Paul in the area of speaking, yet in acting they both worked together.

He further adds that he had received praise, not from one individual or even from one Church alone, but from all the Churches. To this general testimony, he adds a particular one fitting for the matter at hand—that he had been chosen for this role by the approval of the Churches. It was likely that this honor would not have been bestowed on him if he had not long before been known to be qualified for it. We must observe, however, the method of election—that which was customary among the Greeks—χειροτονία (a show of hands), in which the leaders led with authority and counsel and guided the entire process, while the common people indicated their approval.