Charles Ellicott Commentary 1 Corinthians 14:13

"Wherefore let him that speaketh in a tongue pray that he may interpret." — 1 Corinthians 14:13 (ASV)

In an unknown tongue.—Better, in a tongue. The gift of interpretation would make the gift of tongues useful for edifying the Church. This would be an object of unselfish prayer, which God would indeed answer. In the Greek, it is suggested that the gift of interpretation is not only to be the object of his prayer, but that it will also be the result; and this leads to the thought in the next verse.