1 Corinthians 14:9
So it is with you, if you speak words [in an unknown tongue] that are not intelligible and clear, how will anyone understand what you are saying? You will be talking into the air [wasting your breath]!
1 Corinthians 9:26
Therefore I do not run without a definite goal; I do not flail around like one beating the air [just shadow boxing].
Treasury of Scripture Knowledge
Summary
So likewise ye, except ye utter by the tongue words easy to be understood, how shall it be known what is spoken? for ye shall speak into the air.
Easy
Bible References
Easy
1 Corinthians 14:19
nevertheless, in public worship I would rather say five understandable words in order to instruct others, than ten thousand words in a tongue [which others cannot understand].
For
1 Corinthians 9:26
Therefore I do not run without a definite goal; I do not flail around like one beating the air [just shadow boxing].