Isaiah 16:6

Here we have, I. The sins with which Moab is charged, Isa 16:6. The prophet seems to check himself for going about to give good counsel to the Moabites, concluding they would not take the advice he gave them. He told them their duty (whether they would hear or whether they would forbear), but despairs of working any good upon them; he would have healed them, but they would not be healed. Those that will not be counselled cannot be helped. Their sins were, 1. Pride. This is most insisted upon; for perhaps there are more precious souls ruined by pride than by any one lust whatsoever. The Moabites were notorious for this: "We have heard in both ears of the pride of Moab; it is what all their neighbours cry out shame upon them for. He is very proud; the body of the nation is so, forgetting the baseness of their origin and the brand of infamy fastened upon them by that law of God which forbade a Moabite to enter into the congregation of the Lord for ever, Deu 23:3. We have heard of his haughtiness and his pride. It is not the rash and rigid censure of one of two concerning them, but it is the character which all that know them will give of them. They are a proud people, and therefore they will not take good counsel when it is given them.

— Matthew Henry's Concise Commentary (public domain)

We--Jews. We reject Moab's supplication for his pride. lies--false boasts. not be so--rather, "not right"; shall prove vain (Isa 25:10; Jer 48:29-30; Zep 2:8). "It shall not be so; his lies shall not so effect it."

— Jamieson-Fausset-Brown Commentary (public domain)