This gift was in the early church, and was a sign “to them that believed not,” in fulfillment of Isaiah 28:11-12; compare 1 Corinthians 14:21. The gift was exhibited in a special way on the day of Pentecost, when people of many lands heard the wonderful things of God each in his own language. In the assembly these gifts were not to be exercised unless there was present an interpreter, that the saints might be edified. Paul thanked God that he spake with tongues more than all at Corinth; but in the assembly he would rather speak five words through his understanding, that he might teach others, than ten thousand words in a tongue (1 Cor. 12:10,28,30; 1 Cor. 13:1,8; 1 Cor. 14:2-39).
The expression “unknown tongue” is unhappy, because it has led some to think that the gift of tongues consisted of a sort of unintelligible gibberish. The word “unknown” has been added in the AV, where it should read simply “tongue.” At Pentecost it was shown that the gift of “tongues” was in a person speaking a language which he had never learned, but which was at once understood by those who knew it.