What does 2 Kings 18:19 mean?

The Assyrian field commander said to them, 'Tell Hezekiah: The great king of Assyria wants to know—what are you relying on?','commentary':'The Assyrian spokesman questions Hezekiah’s confidence, trying to undermine his trust and make him doubt his choices.'} ,{ 2 Kings 18:19 - Modern Text Bible

(The Assyrian spokesman questions Hezekiah’s confidence, trying to undermine his trust and make him doubt his choices.)