1 Corinthians 14:22
22 So then tongues are for a 1sign, not to those who believe but to the unbelievers; but prophecy is for a sign not to the unbelievers but to those who believe.
221 So then at the beginning of this verse indicates that according to the word in v. 21 quoted from Isa. 28, tongues are for a negative sign to the unbelievers, signifying their poor condition of unbelief. It implies that wherever a strange tongue is spoken, people's unbelief is there. The apostle's intention here was to hold the Corinthians back from their excessive practice of speaking in tongues. But prophecy is for a positive sign to those who believe, signifying their proper condition of belief. This is an encouragement to the practice of prophesying.