1 Corinthians 14:21-25

21It is written in the Law, “By men of strange tongues and by the lips of foreigners I will speak to this people, and not even then will they listen to Me,” says the Lord.

22Therefore, [unknown] tongues are [meant] for a [supernatural] sign, not to believers but to unbelievers [who might be receptive]; while prophecy [foretelling the future, speaking a new message from God to the people] is not for unbelievers but for believers.

23So then, if the whole church gathers together and all of you speak in [unknown] tongues, and outsiders or those who are not gifted [in spiritual matters] or unbelievers come in, will they not say that you are out of your mind?

24But if all prophesy [foretelling the future, speaking a new message from God to the people], and an unbeliever or outsider comes in, he is convicted [of his sins] by all, and he is called to account by all [because he can understand what is being said];

25the secrets of his heart are laid bare. And so, falling on his face, he will worship God, declaring that God is really among you.