1 Corinthians 14:21

In the law it is written, By men of strange tongues and by the lips of strangers will. speak unto this people; and not even thus will they hear me, saith the Lord.

'In the law it is written'. Isaiah 2:11. Yes, the book of Isaiah was God's "law" also. Actually the whole O.T. was called God's law. (1 Corinthians 14:34; John 10:34; Romans 3:19)

'The setting is clear. The people won't hear the words of the prophet (who speaks to them in their own language) so God will speak to them in the language of the Assyrians (if you think Israel is in view) or Babylonians (if you think Judah). Had they listened to the prophets they wouldn't have needed foreign chastizement. But they wouldn't listen so they will go into captivity. And in captivity they will be reminded of their unbelief by the daily "babbling" (of foreign dialects) going on all around them. It was unbelief that necessitated the lesson of the foreign language.' (McGuiggan p. 182)