How does McCarthy set up the book's major irony in this chapter?

This section sets up the great irony that will be the main feature of the story: the budding relationship between Sylder and John Wesley. Sylder, unbeknown to John Wesley, is Kenneth Rattner's killer, the very man that John Wesley had sworn to exact revenge upon. In their interactions so far, John Wesley has no reason but to be grateful to Sylder.