1 Corinthians 14:2

14:2 For the one speaking in a tongue does not speak to people but to God, for no one understands; he is speaking mysteries by the Spirit.

1 Corinthians 14:15-16

14:15 What should I do? I will pray with my spirit, but I will also pray with my mind. I will sing praises with my spirit, but I will also sing praises with my mind. 14:16 Otherwise, if you are praising God with your spirit, how can someone without the gift say “Amen” to your thanksgiving, since he does not know what you are saying?

1 Corinthians 14:19

14:19 but in the church I want to speak five words with my mind to instruct others, rather than ten thousand words in a tongue.