Easter preceded by Lent is the primary annual cycle of the calendar; secondary to it is Christmas preceded by Advent. This is true both theologically and historically. It is the resurrection that interprets the birth of Jesus. Apart from the resurrection, Jesus has no more claim upon us than Socrates, Abraham Lincoln, Mohandas Gandhi, Martin Luther King, Jr., Anwar Sadat: He was simply one among many good leaders who managed to meet an unjust death.
This theological assertion is buttressed by historical facts: (1) What is presumably the oldest of the four Gospels pays no attention whatever to the birth of Jesus, beginning instead with the account of his baptism; and Paul makes only passing references to Jesus’ birth (as in Galatians 4:4 and Philippians 2:7). Only later did Matthew and Luke attach enough importance to the nativity to comment upon it extensively. (2) Even more significant: Although the resurrection was observed liturgically in the church from its very inception, the earliest recorded liturgical observance of Christmas Day falls well into the fourth century.
—Laurence Stookey, Calendar: Christ’s Time for the Church, 49-50