Charles Ellicott Commentary Isaiah 37:4

"It may be Jehovah thy God will hear the words of Rabshakeh, whom the king of Assyria his master hath sent to defy the living God, and will rebuke the words which Jehovah thy God hath heard: wherefore lift up thy prayer for the remnant that is left." — Isaiah 37:4 (ASV)

Lift up thy prayer for the remnant ... —Isaiah’s characteristic words (Isaiah 1:9; Isaiah 10:21) had impressed themselves on the king’s mind. Now that town after town of Judah had fallen into Sennacherib’s hands (forty-six, according to his inscriptions— Records of the Past, i. 38), those who were gathered within the walls of Jerusalem were as a mere remnant of the people.