Paul pictures a believer giving thanks aloud in a tongue while someone else in the room listens. How can that listener join in with "Amen" if he has no idea what was said? Barnes puts the force of the question this way: "how can he express his assent; how can he join in the act of devotion?" Paul is not doubting the speaker's sincerity. He is pointing to the person beside him who is shut out of the prayer.

The answer is that he cannot. Paul states it directly in the next verse: "For thou verily givest thanks well, but the other is not edified" (1 Corinthians 14:17). He adds his own practice: "I thank my God, I speak with tongues more than ye all: Yet in the church I had rather speak five words with my understanding, that by my voice I might teach others also" (1 Corinthians 14:18-19).

The word "unlearned" is the Greek idiotes, a private or unskilled person. Barnes explains it as someone unacquainted with the foreign language being spoken, "a man in private, in contradistinction from a man in public life." Gill similarly describes one of the common people, as distinct from the one leading in prayer. "Amen" comes from Hebrew and means firm or sure; saying it was how listeners made a prayer their own. Gill notes it was usual among the Jews for the people to say Amen at a blessing, and quotes a Jewish saying: "greater is he that answers Amen, than he that blesses."

The "Amen" shows that worship in the church is meant to be shared. One person may lead in thanks, but everyone present is meant to join and say, in effect, "Yes, this is my prayer too." When the words cannot be understood, that sharing is broken.

Paul's gentle line, "thou verily givest thanks well" (1 Corinthians 14:17), shows that the problem is not the speaker's heart toward God but his neighbor's place in the prayer. Paul has already said that gifts without love leave a person "nothing" (1 Corinthians 13:2).