I have lots of friends to whom I send cards; I know that some are Christian, some are of other faiths and some are atheist/agnostic - and some of them I have no idea whatsoever what their stance on faith might be. I think it's more probable than not that they know that I am a Christian and so to receive a card from me with a Christian theme would be no surprise at all and most certainly would not cause offense to any of them.
We actually invited two of our close muslim friends to spend Christmas with us this year and although they were unable to accept they were delighted to be asked.
Passports not in the drawer I always keep them in. Turning the place upside down.