John Calvin Commentary 1 Corinthians 14:24

"But if all prophesy, and there come in one unbelieving or unlearned, he is reproved by all, he is judged by all;" — 1 Corinthians 14:24 (ASV)

But if all prophesy—as he had previously shown them how much more advantageous prophecy is to those that are of the household of faith (Galatians 6:10) than the gift of tongues, so he now shows that it would also be useful to those that are without (1 Corinthians 5:13). This is a most powerful consideration for showing the Corinthians their error.

For what a shameful thing it is to devalue a gift that is most useful both to believers and unbelievers, and to be completely absorbed by another gift which is useless to those within the church and, in addition, causes offense to those without. He presents this advantage of prophecy to them: that it summons the consciences of the wicked to God's tribunal and strikes them with such a vivid realization of divine judgment that the one who previously, in complete disregard, despised sound doctrine is compelled to give glory to God.

We will find it much easier to understand this passage, however, if we compare it with another that occurs in the Epistle to the Hebrews (Hebrews 4:12).

The Word of God is quick and powerful, and sharper than any two-edged sword; piercing to the dividing asunder of soul and spirit, and of the joints and marrow — a discerner of the thoughts of the heart.

For in both passages, the same kind of efficacy of the Word of God is spoken of; only in that other passage, it is spoken of more fully and distinctly. Concerning the passage before us, it is not difficult to understand now what is meant by being convinced and judged.

Men's consciences are in a numb state and are not touched by any feeling of dissatisfaction on account of their sins as long as they are enveloped in the darkness of ignorance.

In short, unbelief is like a lethargy that takes away feeling. But the Word of God penetrates even to the farthest recesses of the mind and, by introducing, as it were, a light, dispels darkness and drives away that deadly numbness.

Thus, then, unbelievers are convinced because they are seriously affected and alarmed when they realize that they have to do with God. Similarly, they are judged in this respect: while they were previously involved in darkness and did not perceive their own wretchedness and baseness, they are now brought into the light of day and are compelled to bear witness against themselves.

When he says that they are judged and convinced by all, you must understand him as meaning all that prophesy, for he had said a little before, If you all prophesy (1 Corinthians 14:24). He has expressly made use of a general term in order to remove the dislike that they felt for prophecy.

The unbeliever, I say, is convinced—not as if the Prophet pronounced a judgment upon him either silently in the mind or openly with the mouth, but because the hearer's conscience perceives his own judgment from the doctrine. He is judged because he descends into himself and, after thorough examination, comes to know himself, while previously he was oblivious to himself.

Relevant to this also is that saying of Christ:

The Spirit, when he is come, will convince the world of sin,
(John 16:8).

And this is what he immediately adds—that the secrets of his heart are made manifest. For he does not mean, in my opinion, that it becomes manifest to others what sort of person he is, but rather that his own conscience is aroused, so that he perceives his sins, which previously lay hidden from his view.

Here again Chrysostom asks how it happens that prophecy is so effectual for arousing unbelievers, while Paul had said a little before that it was not given to them. He answers that it was not given to them as a useless sign, but for the purpose of instructing them. For my part, however, I think that it will be simpler, and therefore more suitable, to say that it was not given to unbelievers, who perish, whose hearts Satan has blinded, that they may not see the light which shines forth from it
(2 Corinthians 4:3–4).

It will also be more fitting to connect this statement with the prophecy of Isaiah (Isaiah 28:11–12), because the Prophet speaks of unbelievers, among whom prophecy is of no profit or advantage.