Easter, Lent and Advent
From the beginning, the main Christian feast was Easter, and this is still true today – Holy Thursday evening through Easter Sunday are the holiest days of the year. And, every Sunday is called a “Little Easter.” (That is why, from early times, penitential actions – such as fasting and kneeling – were prohibited on Sundays, even during Lent.)
The death/resurrection of Jesus took place during the feast of Passover. But there is no way of knowing what time of the year Jesus was born. In the fourth century, the feast of his birth began to be celebrated on December 25, apparently to replace the pagan feast of the “unconquered sun” (the time of year when the days started getting longer again). The feast of the re-birth of the sun was replaced by the feast of the birth of the Light of the World.
Just as there was a time of preparation for Easter (Lent), there also developed a time of preparation for Christmas – Advent. This season varied in length, but eventually the practice of beginning Advent on the fourth Sunday before Christmas became the norm.