I grew up in a Catholic environment, and I still practice Christianity today. For me, I was able to justify my orientation by religious doctrine. There are three vocations that God can call you to be a part of- the religious life, the married life, and the single life- and I see the fact that God made me aro ace as a way to call me into the single life. I don't know how or why I was meant to be single rather than married or religious, but I can feel that I am.
As for how to come out to others in a Christian environment- I don't really know. I think that in a perfect world Christians would accept you for who are because of Jesus' call to love all people, but as you probably know that isn't always the case. I know, for example, my parents are the type to judge people in the LGBT community as being special snowflakes seeing attention, so although I think they'd be okay if I never married, I don't think I can ever really "come out" to them as aro.