I'm not a lawyer, but my understanding is it would depend on what kind of business you're in and what kind of services the Christian customers asked for. You could say "I do websites for weddings, but not Christian weddings" for example.

As I understand it, this ruling still wouldn't necessarily protect broader discrimination like "I own an ice cream shop, but I won't sell ice cream to certain people"; whether the people you're refusing to sell to are Christian, gay, etc...