Does not matter.
Employers can not tell employees how to practice their religion.
Oh it most certainly matters if your 'practice' runs afoul of a generalized policy that the business has against certain behavior. Using your logic, I could walk around my office stoning any adulterers and my boss couldn't fire me because I'm practicing my religion.
Your employer cannot fire you for being a Christian, but they can definitely fire you for doing things that bring discredit on the business as that is a general policy that is not targeted towards Christians.
They can sue if they want, but they will be thrown out of court in short order.
