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.
Related Commentaries of Isaiah 36:4
Isaiah 36:4
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?