It is written, etc.

From Isaiah 28:11, Isaiah 28:12. The quotation does not correspond exactly either to the Hebrew or to the Septuagint. Heb., with stammerings of lip. Sept., By reason of contemptuous words of lips. Paul omits the Heb.: This is the rest, give ye rest to the weary, and this is the repose. Sept.: This is the rest to him who is hungry, and this is the ruin. The point of the quotation is that speech in strange tongues was a chastisement for the unbelief of God's ancient people, by which they were made to hear His voice "speaking in the harsh commands of the foreign invader." So in the Corinthian Church, the intelligible revelation of God has not been properly received.

1 Corinthians 14:21 Parallel Commentaries

the law. The passage quoted is taken from the prophet Isaiah; but the term torah, Law, was used by the Jews to express the whole Scriptures, law, prophets, and hagiographia; and they used it to distinguish these Sacred Writings from the words of the scribes. It is not taken from the LXX., from which it varies as much as any words can differ from others where the general meaning is similar. It accords much more with the Hebrew; and may be considered as a translation from it; 'only what is said of God in the third person, in the Hebrew, is here expressed in the first person, with the addition of [lego kurios,'] saith the Lord.--Dr. Randolph.

John 10:34 Jesus answered them, Is it not written in your law, I said, You are gods?

Romans 3:19 Now we know that what things soever the law said, it said to them who are under the law: that every mouth may be stopped...

With.

Deuteronomy 28:49 The LORD shall bring a nation against you from far, from the end of the earth, as swift as the eagle flies...

Isaiah 28:11,12 For with stammering lips and another tongue will he speak to this people...

Jeremiah 5:15 See, I will bring a nation on you from far, O house of Israel, said the LORD: it is a mighty nation, it is an ancient nation...