Charles Ellicott Commentary 1 Corinthians 14:23

"If therefore the whole church be assembled together and all speak with tongues, and there come in men unlearned or unbelieving, will they not say that ye are mad?" — 1 Corinthians 14:23 (ASV)

If therefore.—Intended, as tongues were, for a “sign,” they cease to be so useful if not properly employed. The report of the strange utterances that take place in the assembled Church may lead some unbeliever to come there; but if there are tongues alone, and they are uninterpreted, the stranger will simply think those present are mad .

It is not meant here that all commence shouting out at the same time, nor does the next verse imply that all prophesy simultaneously. Instead, the thought presented is the undue and exclusive cultivation of this gift by all in the Corinthian Church.