A.T. Robertson 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 (συνεπεμψαμεν μετ' αυτου). Epistolary aorist.

The brother (τον αδελφον). This may be, probably is, Luke who may also be the brother of Titus according to a common Greek idiom where the article is used as "his." But this idiom is not necessary. As a matter of fact, we do not know who this brother is.

Is spread through all the churches (δια πασων των εκκλησιων). No verb in the Greek (ellipsis).