Pages 1-3 simply show that (c-a) and (b-a) divide (a+b-c)^n (for even n), assuming they are a solution to FLT.
You then define g to be (a+b-c)^n/(c-a)(b-a), an integer.
I follow you this far. I do not see why g divides a+b-c, and I don't think the argument on p.4 proves it.