Charles Ellicott Commentary Isaiah 37:26

"Hast thou not heard how I have done it long ago, and formed it of ancient times? now have I brought it to pass, that it should be thine to lay waste fortified cities into ruinous heaps." — Isaiah 37:26 (ASV)

Hast thou not heard ... —The speech of Sennacherib ends, and that of Jehovah begins. The adverb “long ago” should be connected with the words that follow. The events of history had all been foreseen and ordered, as in the remote past, by the counsels of Jehovah. Kings and armies were merely as His puppets in the drama of the world’s history.

The words “Hast thou not heard” suggest that Isaiah assumes Sennacherib had heard of his prophecies, or those of his forerunners, concerning the purposes of Jehovah—an assumption that, given he had ministers who were well acquainted with Hebrew (Isaiah 36:12), was itself quite probable.