I have spent years playing with friends, admittedly it's been a few years, and now I'm jumping back in with 5th edition.  I've got a very rough idea of a campaign but for obviously reasons I can't kick around ideas with the friends who would be playing the campaign.  I'm looking or some experienced DM's that might offer another perspective to fully realize the campaign.

In broad strokes here is the rough idea.

I want to make a growing religious organization with plans to supplant the pantheon of gods. (probably based in typical forgotten realms)  I would like to model the religious organization off of christian biblical stories.  (I'm not a religious person I'm sorry if that offends.)  Some of my initial thoughts would be finding books in a language they can't read. (Aramaic)  Notice street gatherings of followers that spark intrigue.  Maybe even include quests for items like the shroud of torah, ark of the covenant and spear of destiny.

Ultimately the final conclusion would be either a God, one of forgotten realms, that has concealed him/herself in order to recruit the followers of all the others.  Or, a very powerful person with the scheme to make himself a diety.

The part that I'd like to talk to people about is the mechanics of how I could conceal all of that in such a way that even if they say found the shroud of torah they don't realize exactly what it is that they're carrying until much further into the campaign.

I'm open to any suggestions, ideas, or advice.

Thanks for listening

Obviously using a different name for the item is the first step, you tell your players they're searching for the ark of the covenant and someone will ultimately make Indiana Jones references.

Secondly, you don't tell them any more than they need to know. One of my favorite lines I use when talking to other DMs is "Players are dumb, because we make them dumb". Players only know, truly know, anything when the DM tells them as much. If your player says "That's a vampire, let's show a crucifix, that'll scare it!" that only holds true if you, as the DM, say that it is effective. So if your quest giver say's it's an important religious artifact, he doesn't have to explain that it houses the potential to upset the pantheon. 

Thirdly, make learning about the item extremely difficult. If the players are going to do research into what they're attempting to find, let them. They'll soon find out that the history of this item is all but lost to time and obfuscation. Throw them a morsel that complements the "important artifact" bit, but you don't have to give them anything more than "very spiritual" or "artifact of the gods". It remains vague and at the same time gives the impression that it has great value.

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In the end presentation, narrative, and properly picked words will make the hidden agendas work for you.

I completely follow that and planned on doing something like that.  My biggest concern is trying to come up with clues and such that won't give it away too early.  What I might think is subtle might turn out to be incredibly obvious then that kind of ruins the rest of the campaign as set out.  

I guess more than advice I'm looking for suggestions on plot devices.  

The idea that I've been kicking around for the beginning of all of this would be to investigation an apparent "lich" siting.  The story would be vaguely that out side of town there are stories of an executed man being brought back from the dead.  I haven't decided if I should actually have that be the case or if it was simply a story that was created to begin the creation of the religious organization.  The problem with that is that I start with the all too obvious shroud of torah.  Regardless of what I say about it I'm concerned that the group investigating an apparent resurrection find a dirty cloth with the vague imprint of face could give it all away right there.

I think you could get away with bible stories.  Using only artifacts that center on the Messiah, though, that would be either very difficult to obfuscate for you or very easy for players to figure out.  Once that part is figured out... you have to then find a way to work it all in, and you are in a Meta-Swamp of religion. Using the story elements from the old testament, though, there is some gold in those hills that your players aren't going to figure out very easily.  And if they do, well, kudos to them... it isn't going to be turned into a meta morass that they are fighting with themselves and you about.  Now, if you want to go the whole black cross, shroud route... then look further into the Dark Ages Vampire system.  

Alternatively, you could go for a hunt for an NPC like Casca (book series) and the spear of Longinus.  If you went back in time and found the point where a mortal was raised to deity (whatever level), then you have a moment in time you could build this NPC in.  They cannot die from a curse given to them at the time and there are long series of lives that they have lived but had to give up because they had to escape persecution or lost the business or lost loved ones that caused them to change.  What is different from their account than what has been written in recorded histories?  Is their memory what it once was or have they forgotten parts of the story too?