First Isaiah, Chapters 36 to 39 - Who Did Thet Cut and Paste?

First isaiah, though largely takin place in the eighth century, is actually it's a weaving together of scenes from two different time periods. chapters 36 to 39 seem to be cut and pasted from second kings 18 to 20 almost in its entirety. Second isaiah assumes the reality of the exile. It assumes that it's already a thing. The exile is not in the future. It's a present reality.