You ain't get it?
You going to get through the internet site below with cheats, hints and walkthroughs.
http://gamefaqs.com

And especially for Messiah:
http://gamefaqs.com/pc/62551-messiah

I am having trouble with (what I assume to be) the final battle of the game with Satan. I already check the walkthroughs in Gamefaqs: one is excellent but only finished about half-way, while the other is too brief and *ahem* confusing at best.

So any tips on the final battle? I always got killed by Satan's ... what do you call it, killing wave?