AUTHORSHIP OF THE BOOK OF ISAIAH
There are three distinct timelines in Isaiah, and the time between them is so great that they couldn't have been written in the present by the same person. While other prophets talk about the future, Isaiah seems to talk in the future. Scholars have developed a variety of theories to explain the gaps in the timeline and the stylistic changes. While there is wide agreement about the evidence, there isn't as much consensus on what to do with that evidence. Scholars generally divide Isaiah into three distinct sections based on the changes in the timeline, assuming that there were at least three authors. Presumably, Isaiah ("proto-Isaiah") wrote chapters 1-39, an anonymous author living during the exile ("deutero-Isaiah") wrote 40-55, and another anonymous author living after the exile ("trito-Isaiah") wrote 56-66. These authors are also referred to as First Isaiah, Second Isaiah, and Third Isaiah.
Many scholars argue that Isaiah was the original source for all 66 chapters, but that the book was assembled over the years from his collected works: his speeches, sermons, talks, and comments.
Isaiah is the only author represented in the book. As far as we know, the book has always existed as a single collection, and it has always been called Isaiah. The oldest copy of Isaiah we have is from the Dead Sea Scrolls, dated from around 175 BC. It's a single scroll from end to end, with no divisions or signals from a copyist that there is some sort of change between chapter 39 and 40.
While scholars disagree about exactly how to interpret the signs of multiple authors, there's a common thread: the prophet Isaiah wrote the book of Isaiah-with help. It's possible that it is simply a collection of his written and spoken words. It's also possible that his original writings were expanded on by later priests living during and after the exile.
Either way, the book has been preserved in this form since ancient times, and both Jewish and Christian traditions accept it as the inspired Word of God.
