Isaiah 37:18 - Ellicott's Commentary On The Whole Bible

Of a truth, Lord... — The facts of Rabshakeh’s induction are admitted, but the inference denied, on the ground that the cases were not parallel. The gods of the nations had been cast into the fire (an alternative to their being taken as trophies for the temples of Asshur and Ishtar), but this could never happen to Jehovah, of whom there was no graven image, and He would show that He alone was ruler of the earth and of the heavens.