"But they held their peace, and answered him not a word: for the king's commandment was, saying, Answer him not. Then came Eliakim, the son of Hilkiah, that was over the household, and Shebna the scribe, and Joah, the son of Asaph, the recorder, to Hezekiah with their clothes rent, and told him the words of Rabshakeh." (Isaiah 36:21-22)
Some words do not deserve a reply. Hezekiah's messengers would have been wasting their time to answer such an arrogant fool. The Almighty would answer these arguments Himself. Besides, what was there to say? The sins of Judah had brought this situation upon her. God was using this Assyrian rod, and only He could break it when its arrogance exhausted its usefulness. The messengers showed wisdom in their actions. They rent their clothes in humility and fear for what had been spoken against the Lord. Their actions demonstrated an acknowledgment of their inability to help themselves and their dependence upon the One Who can work the impossible. At this juncture, they and their king had no recourse but to take Rabshakeh's words to God and remember the words of Isaiah spoken many years prior.
Wherefore it shall come to pass, that when the Lord hath performed his whole work upon mount Zion and on Jerusalem, I will punish the fruit of the stout heart of the king of Assyria, and the glory of his high looks. For he saith, By the strength of my hand I have done it, and by my wisdom; for I am prudent: and I have removed the bounds of the people, and have robbed their treasures, and I have put down the inhabitants like a valiant man: And my hand hath found as a nest the riches of the people: and as one gathereth eggs that are left, have I gathered all the earth; and there was none that moved the wing, or opened the mouth, or peeped. Shall the axe boast itself against him that heweth therewith? or shall the saw magnify itself against him that shaketh it? as if the rod should shake itself against them that lift it up, or as if the staff should lift up itself, as if it were no wood. Therefore shall the Lord, the Lord of hosts, send among his fat ones leanness; and under his glory he shall kindle a burning like the burning of a fire (Isaiah 10:12-16).