Why is the idea of multiple authorship so destructive?
Those of us to whom the Living God has made known his existence have no doubt of His great love and Sovereignty. This broken world is not a closed system and the Bible is a source of light flowing to us from God. For these reasons and the Bible’s historically demonstrated truth, Christians throughout the ages have held to belief in inspiration of the Scriptures. The idea that Isaiah was written by a committee over a couple hundred years is destructive to the understanding of the Sovereignty of God and His ability to communicate in advance His eternal plan for our salvation. I have been on a lot of committee’s and I do not remember any of them being inspired!
It is clearly unfair to lump all multiple author scholars into a single bucket, or categorize someone on the basis of one position, and we should never do so. However, the idea of multiple authorship itself has been detrimental to the culture as denominations have drifted away from the Old Testament. But God is graceful, and we are to be so as well. Scholars are, and will be, returning to the idea of single authorship, and many more will do so, and they are to be welcomed with open arms. In most cases is not a matter of salvation, and like everyone else, theologians need to encourage each other in the faith of God who inhabits eternity.
Having said that, in putting forth a literary structure, it is probably inevitable that a few individuals will just try to cut the Book up in a different way, perhaps even along the very lines of the way that Isaiah organized the book. We should recognize and say in advance that yet another way of trying to cut up Isaiah would be completely illogical.