Albert Barnes Commentary Isaiah 37:35

"For I will defend this city to save it, for mine own sake, and for my servant David`s sake." — Isaiah 37:35 (ASV)

For I will defend this city - Despite all that Hezekiah had done to put it in a posture of defense (2 Chronicles 32:1 and following), it was still Yahweh alone who could preserve it.

For my own sake - God had been reproached and blasphemed by Sennacherib. As His name and power had been blasphemed in this way, He says that He would vindicate Himself and, for the honor of His own insulted majesty, would save the city.

And for my servant David’s sake - On account of the promise which He had made to him that there should not fail a man to sit on his throne, and that the city and nation should not be destroyed until the Messiah should appear .