In church means “in a meeting of Christians” (see the comments on 1 Cor. 14.4).

With my mind, as in verse 15, probably means “with my understanding.” Good News Bible has tried to make this clearer by saying “that can be understood.” This is probably a better translation, as nonecstatic speech is speech that can be understood.

Quoted with permission from Ellingworth, Paul and Hatton, Howard A. A Handbook on Paul’s First Letter to the Corinthians, 2nd edition. (UBS Handbook Series). New York: UBS, 1985/1994. For this and other handbooks for translators see here .