Since it's the Monday after Christmas, I thought we'd take a brief tour of salvation history today.
(And yeah, I do mean brief. We're not going to spend 40 years with the Israelites, today.)
In short: Jesus didn't need to be born. Until humans screwed things up.
When God created Adam and Eve, everything was perfect. Adam and Eve were in a state of grace--and they would never die, either, when God first created them.
Then...they ate that fruit. And things changed.
As Milton says:
Of Man's first disobedience, and the Fruit
Of that Forbidden Tree, whose mortal taste
Brought Death into the World, and all our woe,
With loss of Eden, till one greater Man
Restore us, and regain the Blissful seat.
--Paradise Lost, Book 1, 1-5
"God so loved the world that he sent his only son, so that all who believe in him might not perish, but have eternal life." (John 3:16)
Jesus was born to Mary, in a stable in Bethlehem, so he could die for us, and redeem us.
We celebrate Christmas because it's the birthday of Christ--it's the beginning of our redemption, it's the Incarnation--God made man, Emanuel (God with us). But in order for us to be redeemed, Jesus has to die. He can't just come and be born. Mary knows that when she presents the baby Jesus in the temple and Simeon tells her a sword shall pierce her heart. The cross is always there.
But at Christmas, we celebrate the birth of that perfect child, the God-man, who has come and taken on human flesh out of sheer love for us.
Christmas, really, is all about love.