Paul adds a second picture, this time one where unclear sound is not just useless but dangerous. A soldier depends on the trumpet to know what to do. If its call cannot be read, no one gets ready. Barnes lists the trumpet's uses in war: "to summon the soldiers; to animate them in their march; to call them forth to battle; to sound a retreat." He explains that an uncertain sound "was one in which none of these things were indicated, or in which it could not be determined what was required." Barnes applies it to their assembly: foreign tongues spoken there would be just as useless "in regard to their duty, their comfort, and edification."

The answer is obvious: no one. Paul then applies the picture directly: "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" (1 Corinthians 14:9). He has already said that the one who prophesies speaks "unto men to edification, and exhortation, and comfort" (1 Corinthians 14:3), which is the kind of clear call the church needs.

Gill notes that "the sound of the trumpet was the alarm of war," and that Jews and other nations used it to gather soldiers and prepare them for battle. The Greek word for "uncertain" is adelos, meaning indistinct or unclear. The verb "prepare himself" (paraskeuazo) means to make ready. Gill also applies the picture to preaching: when the message of salvation is muddled, he says, hearers are left in uncertainty and confusion.

Gill sees in the trumpet a picture of the gospel, whose use is "to prepare and animate them for battle, with their spiritual enemies." Clear words from God's people help others know what to do: to come, to stand, to move forward. That is why Paul values prophecy, which speaks "to edification, and exhortation, and comfort" (1 Corinthians 14:3).

The question also reflects God's own way of speaking. Paul will soon say that "God is not the author of confusion, but of peace" (1 Corinthians 14:33). The God who gives His people gifts wants those gifts to sound a call His people can understand and answer.