Charles Ellicott Commentary Isaiah 36:15-16

"neither let Hezekiah make you trust in Jehovah, saying, Jehovah will surely deliver us; this city shall not be given into the hand of the king of Assyria. Hearken not to Hezekiah: for thus saith the king of Assyria, Make your peace with me, and come out to me; and eat ye every one of his vine, and every one of his fig-tree, and drink ye every one the waters of his own cistern;" — Isaiah 36:15-16 (ASV)

Neither let Hezekiah make you trust in the Lord ... —Rabshakeh had apparently heard from spies or deserters of Hezekiah’s speech to his people (2 Chronicles 32:7–8).

In contrast with what he derides as trust in a God who was against those who trusted Him, he offers tangible material advantages. They have only to leave the besieged city and go to the Assyrian camp, and they will be allowed provisionally to occupy their own houses and till their own fields; and, instead of dying of thirst, each man will have the waters of his own cistern.

Then, not without a latent sarcasm—worse than the vae victis, which is the normal utterance of conquerors—he offers the doom of exile as if it were a change for the better and not the worse, as though the conquered had no love of country as such, no reverence for the tombs of their fathers, and no yearning for the Temple of their God.

The taunt and the promise may, perhaps, be connected with Sennacherib’s boast that he had improved the water-supply of the cities of his empire (Records of the Past, i. 32, 9:23, 26, 28).