1 Corinthians 14:9 - Ellicott's Commentary On The Whole Bible

So likewise ye. — This is not the application of the foregoing, but the introduction of a third illustration, viz., the varieties of human language. The “tongue” here is simply the actual organ of speech, distinguished in the Greek, by the insertion of the article, from “tongues” which flow from the spiritual gift. If a human being does not use words that those spoken to understand, it is useless; such words pass as sounds into the air and are useless.