While I haven't read the fic itself (and would definitely prefer to avoid doing so), I did just read the TVTropes page on it (which is extremely informative), and while I agree with the Legendary status...I don't think this is quite right for PPCing.
You've said that the a/ns are the part about religion, but the Tropes page says it's got Author Tract, the (or a?) main character "attempting to convert the Clans to Christianity", a version of the Ten Commandments playing a role in the story, Starkit (I assume this is the kit who becomes StarGleam) actually being called, in-fic, the cats' 'savor' and Jesus, I am not kidding--look, just take a look through the Tropes page. It's very informative, and has a lot of quotes. I'd say it's probably giving a very good idea of what the fic is like; TVTropes pages on badfics tend to, and this one looks pretty thorough to me.
What does the PPC say about this? Well, let's take a look:
What about religious fic?
As noted in the Guide to the PPC, we consider fanfiction based on religious texts to be in poor taste, and since a mission is a form of fanfic, we'd be hypocrites to PPC such fics. It happened once, but after that we agreed as a community not to go there again.
Then there's fanfic that has overt religious themes while not strictly being a religious-text-fic. Sporking religious fanfic is tricky – so tricky that it's best just to leave it alone. We've seen those fics where Harry Potter converts to Christianity, and we find them just as mind-boggling as you do, but we prefer not to run the risk of offending or hurting our fellow Boarders by accidentally bashing someone's religion while sporking a story.
That doesn't mean you can't PPC any fic that so much as mentions a religion or contains a religious character, but please exercise extreme caution and remember that everyone has a right to their own beliefs, even if you don't agree with them.
Personally, I think that this looks like exactly the sort of badfic we do not take on. Religion seems to play a pretty big part in it--particularly religion of the Author Tract!Missionary sort, which, er, is pretty out of place in the Warriors-verse, I'll give you that--and by 'it' I mean both the a/ns and the story itself. It looks like it'd be really difficult to PPC without offending people, and, quite honestly, it doesn't look like the kind of fic we spork. Library of the Damned would do it--they did Prayer Warriors, after all, and it went pretty well--but I'm pretty sure it's not for us.
So: as horrible as it is, as horrible as even the non-religious elements are...I'd recommend leaving it alone. PPCing it looks like a horrible idea to me, and I'm pretty sure I'm not the only one with that opinion.
(Legendary status, though? I'm on board with that. Very much so. Unless Legendary status is limited to non-religious-element badfics?)
~DF