14:20 Brethren, do not be children in understanding; however, in malice be babes, but in understanding be mature.
21 In the law it is written:
“With men of other tongues and other lips
I will speak to this people;
And yet, for all that, they will not hear Me,”
says the Lord.
22 Therefore tongues are for a sign, not to those who believe but to unbelievers; but prophesying is not for unbelievers but for those who believe. 23 Therefore if the whole church comes together in one place, and all speak with tongues, and there come in those who are uninformed or unbelievers, will they not say that you are out of your mind? 24 But if all prophesy, and an unbeliever or an uninformed person comes in, he is convinced by all, he is convicted by all. 25 And thus the secrets of his heart are revealed; and so, falling down on his face, he will worship God and report that God is truly among you.
Continuing along the same teaching Paul goes one step further to illustrate to them how much they have missed the mark. Quoting a promise from the Old Testament he shows that the gift of speaking other languages was given by God to reach unbelieving foreigners. Language is both a bridge and a barrier. A language that is understandable is a bridge. An unknown language is a barrier. God promised that He would overcome the language barrier. He would provide a way for those of other languages to hear the gospel even some still would not listen.
Paul is demonstrating that the gift of tongues (languages) was given for a very specific and practical reason. It was to take down the barrier of language and build a bridge of understanding and gospel opportunity to those from other places who could not understand Hebrew, Aramaic, or the Greek language. On the other hand prophecy was a gift designed for believers. When we think of the prophets in the Bible their calling was always to lead, guide, and instruct those who already believed.
Then Paul turns the tables to show how badly they have been abusing the gift of tongues. He says imagine if a visitor walked into your church and everyone is speaking in a different language all at the same time? They won't learn anything. No barrier will be taken down. No bridge will be built. They will leave convinced you have all lost your minds.
On the other hand if they came in and heard a prophetic teaching in a language they understood they would be convicted by what they heard and maybe even drawn to worship our God who knows the end from the beginning.
So a gift meant for believers could make an unbeliever believe if uses properly while the very gift designed to reach that same unbeliever will turn him away if uses the wrong way.
The lesson is again obvious. It's not so much about what gift(s) you have or don't have but how, when, and where you use them. Remember we were gifted to serve God and others, not to serve ourselves. Selfishness in any form turns others away. The church does not exist to please itself. A selfish church focused entirely inwardly is perfectly positioned to turn every visitor back out the same door they came in.
Whenever God rebukes His church it is for the sin of selfishness and the ignoring of those in need. This tongues mess was exactly that in Corinth. They gathered to show off their "holy talents" while the confused and lost community looked on in bewilderment and walked away empty and more lost than before they came.
Do you draw lost people or repel them? If you repel them you may want to reconsider how you are using your gift(s).