1 Corinthians 14:9

New American Bible - revised edition

Similarly, if you, because of speaking in tongues, do not utter intelligible speech, how will anyone know what is being said? For you will be talking to the air.

Cross References

1 Corinthians 14:10

It happens that there are many different languages in the world, and none is meaningless;

1 Corinthians 9:26

Thus I do not run aimlessly; I do not fight as if I were shadowboxing.