Albert Barnes 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)

Yet in the church. In the Christian assembly. The word church does not refer to the edifice where Christians worshipped, but to the organized body of Christians.

I had rather, etc. It is probable that in the Christian assembly, usually, there were few who understood foreign languages. Paul, therefore, would not speak in a foreign language when its only use would be mere display.

With my understanding. So as to be intelligible to others; so that I might understand it, and so that at the same time others might be benefited.