Albert Barnes Commentary 2 Kings 19:15

"And Hezekiah prayed before Jehovah, and said, O Jehovah, the God of Israel, that sittest [above] the cherubim, thou art the God, even thou alone, of all the kingdoms of the earth; thou hast made heaven and earth." — 2 Kings 19:15 (ASV)

You who dwell between the cherubim - The reference is to the Shekinah, or miraculous glory, which appeared from time to time above the mercy seat from between the two cherubim, whose wings overshadowed the ark of the covenant (1 Kings 6:23–27; Leviticus 16:2 and following).

You are the God, you alone - This is the protest of the pure theist against the intense polytheism of Sennacherib’s letter, which assumes that gods are only gods of particular nations, and that Hezekiah’s God is but one out of an indefinite number, no stronger or more formidable than the rest.