What does 2 Kings 20:6 mean?

I’ll give you fifteen more years to live. I’ll also save you and this city from the king of Assyria. I’ll protect this city for my own sake and because of my promise to David.' 2 Kings 20:6 - Modern Text Bible

(God not only extends Hezekiah’s life but also promises to defend Jerusalem, tying His actions to His faithfulness to David.)