Speaking in Tongues = Speaking in Parables.
A correlation exists between 1 Corinthians 14:21 and Isaiah 28:11. This links the two accounts.
-- New American Standard 1 Corinthians 14:21 In the Law it is written, "By men of strange tongues and by the lips of strangers I will speak to this people, and even so they will not listen to Me," says the Lord.
-- New American Standard Isaiah 28:11 Indeed, He will speak to this people Through stammering lips and a foreign tongue,
In Isaiah chapter 28 the Message spoken by Isaiah was a parable.
Isaiah speaking --
16. Therefore thus saith the Lord God, Behold, I lay in Zion for a foundation a stone, a tried stone, a precious corner stone, a sure foundation: he that believeth shall not make haste. 17. Judgment also will I lay to the line, and righteousness to the plummet: and the hail shall sweep away the refuge of lies, and the waters shall overflow the hiding place. 18. And your covenant with death shall be disannulled, and your agreement with hell shall not stand; when the overflowing scourge shall pass through, then ye shall be trodden down by it. 19. From the time that it goeth forth it shall take you: for morning by morning shall it pass over, by day and by night: and it shall be a vexation only to understand the report. 20. For the bed is shorter than that a man can stretch himself on it: and the covering narrower than that he can wrap himself in it. 21. For the Lord shall rise up as in mount Perazim, he shall be wroth as in the valley of Gibeon, that he may do his work, his strange work; and bring to pass his act, his strange act. 22. Now therefore be ye not mockers, lest your bands be made strong: for I have heard from the Lord God of hosts a consumption, even determined upon the whole earth. 23. Give ye ear, and hear my voice; hearken, and hear my speech. 24. Doth the plowman plow all day to sow? doth he open and break the clods of his ground? 25. When he hath made plain the face thereof, doth he not cast abroad the fitches, and scatter the cummin, and cast in the principal wheat and the appointed barley and the rie in their place? 26. For his God doth instruct him to discretion, and doth teach him. 27. For the fitches are not threshed with a threshing instrument, neither is a cart wheel turned about upon the cummin; but the fitches are beaten out with a staff, and the cummin with a rod. 28. Bread corn is bruised; because he will not ever be threshing it, nor break it with the wheel of his cart, nor bruise it with his horsemen. 29. This also cometh forth from the Lord of hosts, which is wonderful in counsel, and excellent in working.
This language of Parables is spoken of in Matthew 13:14 and in Isaiah 6:9.
Jesus gives the reason for speaking in parables in the following verses--
-- New American Standard Matthew 13:14 "And in their case the prophecy of Isaiah is being fulfilled, which says, `You will keep on hearing, but will not understand;
Speaking in parables was Isaiahs directive from the Lord --- the purpose of the gift of tongues is to hide the truths from unbelievers and reveal those same truths to believers. The parable from Isaiah is incomprehensible to unbelievers but believers generally understand the overall meaning of the words.
-- New American Standard Isaiah 6:9 And He said, "Go, and tell this people: `Keep on listening, but do not perceive; Keep on looking, but do not understand.'