What was Christmas originally celebrating?

Explanation

Originally Christmas was a midwinther party that christianity transformed into a party celebrating the birth of Jesus Christ. At a church meeting in the 4th Century the 25th of December was set as the birth date of Jesus Christ.Today´s traditions with Christmas trees, gifts and Santa Claus was developed in the 19th Century but has its roots in the original pagan traditions. Scandinavians still call Christmas for ´jul´.