In the {r} law it is written, With men of other tongues and other lips will I speak unto this people; and yet for all that will they not hear me, saith the Lord.

(r) By the law he understands the entire scripture.

People's New Testament

14:21 In the law it is written. For the quotation, see Isa 28:11,12. The Jews were there told that for their sins they would be carried into the Assyrian captivity, where they would hear strange languages. This was a judgment. Wherefore, do not force the church to listen to listen to strange tongues which serve to remind of the judgment of Israel.

Wesley's Notes

14:21 It is written in the Law - The word here, as frequently, means the Old Testament. In foreign tongues will I speak to this people - And so he did. He spake terribly to them by the Babylonians, when they had set at nought what he had spoken by the prophets, who used their own language. These words received a farther accomplishment on the day of pentecost. Isaiah 28:11.

Jamieson-Fausset-Brown Bible Commentary

21. In the law-as the whole Old Testament is called, being all of it the law of God. Compare the citation of the Psalms as the "law," Joh 10:34. Here the quotation is from Isa 28:11, 12, where God virtually says of Israel, This people hear Me not, though I speak to. them in the language with which they are familiar; I will therefore speak to them in other tongues, namely, those of the foes whom I will send against them; but even then they will not hearken to Me; which Paul thus applies, Ye see that it is a penalty to be associated with men of a strange tongue, yet ye impose this on the Church [Grotius]; they who speak in foreign tongues are like "children" just "weaned from the milk" (Isa 28:9), "with stammering lips" speaking unintelligibly to the hearers, appearing ridiculous (Isa 28:14), or as babbling drunkards (Ac 2:13), or madmen (1Co 14:23).

Matthew Henry's Concise Commentary

14:15-25 There can be no assent to prayers that are not understood. A truly Christian minister will seek much more to do spiritual good to men's souls, than to get the greatest applause to himself. This is proving himself the servant of Christ. Children are apt to be struck with novelty; but do not act like them. Christians should be like children, void of guile and malice; yet they should not be unskilful as to the word of righteousness, but only as to the arts of mischief. It is a proof that a people are forsaken of God, when he gives them up to the rule of those who teach them to worship in another language. They can never be benefitted by such teaching. Yet thus the preachers did who delivered their instructions in an unknown tongue. Would it not make Christianity ridiculous to a heathen, to hear the ministers pray or preach in a language which neither he nor the assembly understood? But if those who minister, plainly interpret Scripture, or preach the great truths and rules of the gospel, a heathen or unlearned person might become a convert to Christianity. His conscience might be touched, the secrets of his heart might be revealed to him, and so he might be brought to confess his guilt, and to own that God was present in the assembly. Scripture truth, plainly and duly taught, has a wonderful power to awaken the conscience and touch the heart.