Albert Barnes Commentary 2 Kings 19:1

"And it came to pass, when king Hezekiah heard it, that he rent his clothes, and covered himself with sackcloth, and went into the house of Jehovah." — 2 Kings 19:1 (ASV)

Hezekiah, like his officers, probably tore his clothes because of Rabshakeh’s blasphemies, and he put on sackcloth in self-humiliation and grief. His only remaining hope was in Yahweh, for Egypt could not be trusted to accomplish anything significant.

Rabshakeh’s boldness had taken its toll on Hezekiah; he was dispirited and dejected. He perhaps began to doubt whether he had done right in yielding to the bolder counsel of Eliakim and Isaiah. He had not lost his faith in God, but it was being severely tested. Wisely, he went to strengthen his faith through prayer.