St. Paul's First Letter to the Corinthians 14:20-25
Brethren, do not be children in your thinking; be babes in evil, but in thinking be mature. In the law it is written, "By men of strange tongues and by the lips of foreigners will I speak to this people, and even then they will not listen to me, says the Lord." Thus, tongues are a sign not for believers but for unbelievers, while prophecy is not for unbelievers but for believers. If, therefore, the whole church assembles and all speak in tongues, and outsiders or unbelievers enter, will they not say that you are mad? But if all prophesy, and an unbeliever or outsider enters, he is convicted by all, he is called to account by all, the secrets of his heart are disclosed; and so falling on his face, he will worship God and declare that God is really among you.