Isaiah 17:4

4.The glory of Jacob shall be diminished. (5) Although he had undertaken to speak of Syria and Damascus, he takes occasion to join Israel with the Syrians, because they were bound by a mutual league, and were united in the same cause. The Syrians, indeed, whom Isaiah chiefly addresses, were like a torch to inflame the Israelites, as we have already said. But the Israelites themselves were equally in fault, and therefore they were justly drawn, by what might be called a mutual bond, to endure the same punishment.

It is not easy to say whether under the name Jacob he speaks of the whole elect people, so as to include also the tribe of Judah. But it is probable that he refers only to the ten tribes, who laid claim to the name of the nation, and that it is in mockery that he describes them as glorious, because, being puffed up with their power and multitude and allies, they despised the Jews their brethren.

And the fatness of his flesh shall wax lean. When he next threatens them with leanness, his object is to reprove their indolence, as the Prophets frequently reprove them for their fatness (Jeremiah 5:28.) On account of their prosperity and of the fertility of the country, they became proud, as horses that are fat and excessively pampered grow restive. Hence also they are elsewhere called “fat cows” (Amos 4:1). But however fierce and stubborn they might be, God threatens that he will take away their fatness with which they were puffed up.