Many of the holidays we celebrate today are considered Christian, but the origins of many modern-day holidays are older than Christianity.
The Christian holiday of Easter commemorates the crucifixion of Christ, and his rise from the dead into heaven. Then where do all the symbolism of bunnies, and eggs come from? It's more than coincedence that the early Pagans had a holiday to mark the Spring Equinox, called Ostara, usually celebrated around March 21st. With the return of spring, came the birthing of the farm animals for the year. Which is why we see bunnies, chicks, eggs and little lambs as symbols for this holiday. Part of the Ostara mythology involved the return of various deities from the underworld (symbolic of the end of winter). So it's not surprising that this holiday got enmeshed with the Christian story of the ressurection of Christ.
Even non-Pagans use the term "Yule" around the Christmas holidays. Yule is celebrated on the Winter Solstice (December 22nd), on the shortest day of the year. Since the days get longer from this point in the year, Yule is a celebration of the returning sun and the rebirth of the God who died at Hallowe'en. As with Easter, the Christian story of the birth of Jesus fits nicely with the Pagan mythology of a God reborn. Traditions such as wreaths and Yule logs are remnants of the original beliefs. Gifts were exchanged at Yule long before the Wise Men offered their gifts to the baby Jesus.
Well, it's not specifically Christian or celebrated as intensely as the two holidays just mentioned, Groundhog Day is still part of the modern-day year. Candlemas (or Imbolc) is celebrated on February 2nd. Because spring is just starting to show itself at this time of year, there were various superstitions about predicting the weather, and how long it would be until the end of winter. The original idea was to watch for a hedgehog, but as people immigrated to North America, the tradition changed to a ground hog to suit local wildlife.
Ok, everyone knows that Hallowe'en is a Pagan holiday, but there are many misconceptions surrounding what the holiday really means. Pagans call the day Samhain (SOW-en or sow-EEN). The old God dies on this day, and the Goddess mourns him until his rebirth at Yule. We use this day to honour and remember our loved ones who have passed on. In an effort to diffuse the interest in this heathen holiday, the Church created All Saint's Day (November 1) as a holy day to recognize all the Catholic saints. But it wasn't a powerful enough idea to wipe out the traditional Hallowe'en celebrattions. Ironically, many Christians do not approve of the celebration of Hallowe'en because of its Pagan origins, not realizing that almost all of the holidays they observe had Pagan beginnings.
Why are major Christian holidays layered on older Pagan festivals? The central reason is that as Christianity was struggling for acceptance in Europe, the country-folk would not give up their age-old traditions. By blending the old with the new, it was easier for the Church to convert the locals.