Albert Barnes 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)

It may be the Lord your God - The God whom you serve, and in whose name and by whose authority you exercise the prophetic office.

Will hear the words - He will come forth and vindicate Himself in regard to the language of reproach and blasphemy that has been used. See a similar use of the word hear in Exodus 2:24; Exodus 3:7.

To reproach the living God - The revilings of Rabshakeh were really directed against the true God. The reproach of the living God consisted in comparing Him to idols, and saying that He was no more able to deliver Jerusalem than the idol-gods had been able to defend their lands (see the note at Isaiah 36:18). The phrase the living God is often applied to Yahweh as distinct from idols, which were mere blocks of wood or stone.

For the remnant that is left - For those who survive; or probably for those parts of the land, including Jerusalem, that have not fallen into the hands of the Assyrian. Sennacherib had taken many towns, but there were many also that had not yet been subdued by him.