1 Corinthians 14:22-25

So you see that speaking in tongues is a sign, not for believers, but for unbelievers. Prophecy, however, is for the benefit of believers, not unbelievers. Even so, if unbelievers or people who don’t understand these things come into your church meeting and hear everyone speaking in an unknown language, they will think you are crazy. But if all of you are prophesying, and unbelievers or people who don’t understand these things come into your meeting, they will be convicted of sin and judged by what you say. As they listen, their secret thoughts will be exposed, and they will fall to their knees and worship God, declaring, “God is truly here among you.”