Why aren't the entire Hogwarts faculty in the Order of Phoenix?

[sephora063]

No: HPFGUIDX 68010

To quote Ryan:
Do you guys think there is a reason that they're not members of the 
order?

That's a good question. Well, the first is that WE don't know whether 
they're part of the Order or not. Part of it is writer's license (and 
talk about nit-picking...but how would have things been different?) 
and perhaps another part of it, is that maybe it's best this isn't 
known to everybody. We know Snape is part of the Order, but we must 
assume that other people don't know and this is best, in order to 
protect his position. Maybe it's best that not everybody is in it. 
Select because they are going behind the MoM's back. Maybe it's just 
the most necessary people.
Dumbledore has to be careful who he chooses (does he choose?) to join 
because of loyalty. I know DD trusts Hagrid with his life (McGonagall 
doubts in SS) and I think that is true for Snape and others. Maybe it 
has something to do with Fawkes. I know someone on another post 
mentioned their wands having the same core( I doubt that), but Fawkes 
is messenger for the Order. You can't be in the Order if the phoenix 
won't even come near you, right? We know the phoenix goes to Harry in 
CoS and Harry was particularly loyal to DD. Does one have to be 
faithful to justice, DD, fighting Voldemort, or what? Or not at all? 
-Sephora