1 Corinthians 14:24 (ESV)

24 But if all prophesy, and an unbeliever or outsider enters, he is convicted by all, he is called to account by all,

Paul now describes a different situation: that of all the church members prophesying. Although he is describing a hypothetical situation, there is a sense in which, even today, everyone who takes part in the worship service can be said to prophesy. When the proclamation of God’s Word is heard and responded to with Amen (1 Corinthians 14:16), and when God is praised in prayer and song, then the church is proclaiming the gospel together (see further Psalm 100:1–5).

The two verbs convicted and called to account are taken from the judicial sphere. When, through the prophesying of church members, an unbeliever hears God’s Word, he can be convicted of its truth and called to account for the sins in his own life. These are things that unintelligible speech cannot accomplish.