Albert Barnes Commentary Isaiah 36:4

"And Rabshakeh said unto them, Say ye now to Hezekiah, Thus saith the great king, the king of Assyria, What confidence is this wherein thou trustest?" — Isaiah 36:4 (ASV)

What confidence—what is the ground of your confidence? On what do you trust? The appellation ‘great king’ was the customary title of the kings of the Persians and Assyrians.