1 Corinthians 14:22-28

Therefore, [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. So 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? But 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]; the secrets of his heart are laid bare. And so, falling on his face, he will worship God, declaring that God is really among you. What then is the right course, believers? When you meet together, each one has a psalm, a teaching, a revelation (disclosure of special knowledge), a tongue, or an interpretation. Let everything be constructive and edifying and done for the good of all the church. If anyone speaks in a tongue, it should be limited to two or at the most three, and each one speaking in turn, and one must interpret [what is said]. But if there is no one to interpret, the one [who wishes to speak in a tongue] must keep silent in church; let him speak to himself and to God.