Albert Barnes Commentary Isaiah 16:6

"We have heard of the pride of Moab, [that] he is very proud; even of his arrogancy, and his pride, and his wrath; his boastings are nought." — Isaiah 16:6 (ASV)

We have heard of the pride of Moab - We Jews; we have “all” heard of it; that is, we “know” that he is proud. The prophet's evident purpose here is to say that Moab was so proud, and was well known to be so haughty, that he would “reject” this counsel. He would neither send the usual tribute to the land of Judea (Isaiah 16:1), thus acknowledging his dependence on them; nor would he give protection to the exiled Jews as they should wander through his land, and “thus” try to win their favor, and secure their friendship. As a consequence of this, the prophet proceeds to state that heavy judgments would come upon Moab as a nation.

He is very proud - The same thing is stated in the parallel passage in Jeremiah 48:29 . Moab was at ease; he was confident in his security; he feared nothing; he sought “no” means, therefore, of securing the friendship of the Jews.

And his wrath - As the result of pride and haughtiness. Wrath or indignation is aroused in a proud man when he is opposed, and when the interests of others are not made to yield to his.

But his lies shall not be so - The Hebrew phrase (לא־כן lo' kên) - ‘not so’ here seems to be used in the sense of ‘not right;’ ‘not firm, or established;’ that is, his vain boasting, his false pretensions, his “lies” shall not be confirmed, or established; or they shall be vain and powerless. In the parallel passage in Jeremiah, it is, ‘But it shall not be so; his lies shall not effect it.’ The word rendered ‘his lies’ here (בדיו badāyv), means his boasting, or vain and confident speaking. In Isaiah 44:25, it is connected with the vain and confident responses of diviners and soothsayers.

Here it means that Moab boasted of his strength and security, and did not feel his need for the friendship of the Jews; but that his security was false, and that it would not turn out according to his expectations. That Moab was proud is also stated in Isaiah 25:8; and that he was inclined to express his pride by reproaching the people of God is apparent from Zechariah 2:8:

I have heard the reproach of Moab,
And the revilings of the children of Ammon,
Whereby they have reproached my people,
And boasted themselves upon their border.