It's fairly obvious that FFX draws a goodly number of references from the Bible. An interesting thesis, but the philosophy of Final Fantasy, and of Squaresoft in general, has tended to revolve around individual rights and freedom of choice rather than faith in anything save oneself. The story hardly lacks a God figure; Yevon is treated as God. Open rebellion against him is held as the only way to save Spira from the mind-numbing dictates of the maesters. Furthermore, Sin is explicitly stated to be the armor of Yevon, this god-figure. This can easily be taken to mean that unless humanity can mentally overcome the antiquated concept of sin and rely solely on reason, we will never progress beyond the spiral of death that persists in a state of ignorance.

Ah, this is why I dislike literary arguments, and indeed the whole of literary analysis; one can make a case for almost anything. I prefer suspension of disbelief, which allows one to make more objective conclusions about a given story based on what's presented.