Jamieson, Fausset and Brown on 2 Kings 18:19

19. Rab-shakeh said--The insolent tone he assumed appears surprising. But this boasting [2Ki 18:19-25], both as to matter and manner, his highly colored picture of his master's powers and resources, and the impossibility of Hezekiah making any effective resistance, heightened by all the arguments and figures which an Oriental imagination could suggest, has been paralleled in all, except the blasphemy, by other messages of defiance sent on similar occasions in the history of the East.