In this chapter Joseph Strorm dies. Why is his death necessary and symbolic?

Gordon Strorm, or "Spider-man," is presented in these chapters as Joseph Strorm's foil. They are almost exactly the same, coming from the same parents, but one was deemed to be abnormal and was banished, while the other, Joseph, falls within the standards of Purity and Norm. They are exact opposites and yet they mirror each other. In these final chapters, the two brothers confront each other in a war, and Gordon kills Joseph, before he himself is killed..... only one of them can remain. This is reminiscent of Cain and Abel from the Bible.