Albert Barnes Commentary 1 Corinthians 14:21

"In the law it is written, By men of strange tongues and by the lips of strangers will I speak unto this people; and not even thus will they hear me, saith the Lord." — 1 Corinthians 14:21 (ASV)

In the law it is written. This passage is found in Isaiah 28:11, 12. The word law here seems to mean the same as revelation, or is used to denote the Old Testament in general. A similar use occurs in John 10:34; John 15:25.

With men of other tongues, etc. This passage, where it occurs in Isaiah, means that God would teach the rebellious and stubborn Jews submission to himself, by punishing them among a people of another language, by removing them to a land—the land of Chaldea—where they would hear only a language that to them would be unintelligible and barbarous. Yet, despite this discipline, they would still be, to some extent, a rebellious people.

The passage in Isaiah has no reference to the miraculous gift of tongues and cannot have been used by the apostle as containing any intimation that such miraculous gifts would be given. It seems to have been used by Paul because the words that occurred in Isaiah would appropriately express the idea he wished to convey (see Barnes on Matthew 1:23) that God would make use of foreign languages for some valuable purpose. But Paul in no way suggests that Isaiah had any such reference, nor does he quote this as a fulfilment of the prophecy; nor does he mean to say that God would accomplish the same purpose by the use of foreign languages which was intended in the passage in Isaiah.

The sense is, as God accomplished an important purpose by the use of a foreign language concerning his ancient people, as recorded in Isaiah, so he will make use of foreign languages to accomplish important purposes still. They shall be used in the Christian church to effect important objects, though not in the same manner, nor for the same end, as in the time of the captivity. What the design of using foreign languages was in the Christian church, the apostle immediately states (1 Corinthians 14:22, 23).

Yet for all that, etc. Despite all this chastisement that will be inflicted on the Jews in a distant land and among a people of a different language, they will still be a rebellious people. This is the sense of the passage as it is used by Isaiah (Isaiah 28:12). It is not quoted literally by the apostle, but the main idea is retained. He does not seem to intend to apply this to the Corinthians, unless it may be to suggest that the power of speaking foreign languages did not necessarily secure obedience. It might be that this power could be possessed, and yet they might be a sinful people; just as the Jews were warned by the judgments of God, inflicted by a people speaking a foreign language, and yet were not reformed or made holy.