Christianism
noun
Chris·tian·ism ˈkris-chə-ˌni-zəm 
ˈkrish-
plural -s
: the religious system, tenets, or practices of Christians
Christianist
ˈkris-chə-nist
noun ˈkrish-
plural Christianists
But it is mistaken to think that even all Christianists feel the need for a nation under Christian law. For many, it is good enough to live in a state that prohibits behaviors at fundamental odds with their faith. 
James G. Poulos, American Spectator, 26 June 2006
James G. Poulos, American Spectator, 26 June 2006 
Word History
Etymology
Middle French christianisme, from Late Latin christianismus, from Greek christianismos, from christianos Christian + -ismos -ism