Nothing..
There is being religious, and then BEING RELIGIOUS, to the point where you try to push it onto the players/ staff etc...
Thats where this becomes an issue (especially with recruits) because some may find that offputting especially since there are many flavors of religion (Judaism, Islam, etc)
I give zero ***** about the religion/beliefs of our coach... I just dont want them to push it on the players...
The same goes for political beliefs...