If a christian won't believe you when you tell them that christmas has pagan roots? Ask them about what "The Twelve Days of Christmas", "Deck the Halls" and/or "We Wish You A Merry Christmas" have to do with christianity.
(HINT: The correct answer is "absolutely fuck-all". All three songs are survivors from pre-christian solstice celebrations. Every single thing your true love gave to you in Twelve Days is a pagan symbol :)