A.T. Robertson Commentary 1 Corinthians 14:19

"howbeit in the church I had rather speak five words with my understanding, that I might instruct others also, than ten thousand words in a tongue." — 1 Corinthians 14:19 (ASV)

Howbeit in church (αλλα εν εκκλησια). Private ecstasy is one thing (cf. 2 Corinthians 12:1–9) but not in church worship.

That I may instruct (ινα κατηχησω). Final clause with ινα. For the rare verb κατηχεω see on Lu 1:4; Acts 18:25.