Isaiah 36:15
Neither let Hezekiah make you trust in the LORD, saying, The LORD will surely deliver us: this city shall not be delivered into the hand of the king of Assyria. Neither let Hezekiah make you trust in the LORD, saying, The LORD will surely deliver us: this city shall not be delivered into the hand of the king of Assyria.
The words are those spoken by Rabshakeh during Assyria's threat against Jerusalem. They were aimed to weaken the people's confidence in Hezekiah. They were aimed to undermine trust in the Lord by insisting that the Lord would not deliver Jerusalem and that the city would fall to the king of Assyria.
He spoke them publicly to frighten the people of Judah and to press them to surrender. His words were a blasphemous challenge to God. The challenge treated the Lord as no different from the powerless gods of the nations Assyria had conquered.