In order to convert the masses, no pun intended, the Church and the Christian leaders took the practice of the people and "bastardized" them into Christian observances. Hence the old Yule practices of the immortal evergreen, the holly, mistletoe, the Sun God being born of the Goddess, were converted to the Christian teachings.Back in the day, the Winter Solstice was on December 25th. But when putting Christmas on the 25th didn't quite stamp out all the other celebrations, the Catholic Church re-engineered the calendar and just happened to move the solstice to the 21st.
It isn't the only celebration they co-opted.
Imbolc, Feb. 2, was originally the goddess Brigit’s day, not to be confused with the Church’s St. Bridget, and Feb. 2 was changed into the Feast of the Presentation of Mary. May 1 is the Pagan celebration of Beltane, and Samhaim, or Halloween, was changed to All Hallows Eve, the eve of the Feast of All Saints.While I'm not Wiccan, I think it crazy to forget that not everyone celebrates your holidays. Wishing them a Merry Christmas isn't offensive, or it shouldn't be, but interrogating them to see if they have their tree decorated or their shopping done is either just plain stupid, or in poor taste. (Almost as bad as pretending observe Hanukkah, but not actually waiting for Hanukkah to begin to do the observing. "Can you image the worldwide rage if the Obamas played fast and loose with a Muslim holiday?")