I've written fourteen small essays that deal with common arguments against the celebration of Advent and Christmas. I've posted a link to all of them here. I hope they help.
And before the LORD your God, in the place that he will choose, to make his name dwell there, you shall eat the tithe of your grain, of your wine, and of your oil, and the firstborn of your herd and flock, that you may learn to fear the LORD your God always. And if the way is too long for you, so that you are not able to carry the tithe, when the LORD your God blesses you, because the place is too far from you, which the LORD your God chooses, to set his name there, then you shall turn it into money and bind up the money in your hand and go to the place that the LORD your God chooses and spend the money for whatever you desire—oxen or sheep or wine or strong drink, whatever your appetite craves. And you shall eat there before the LORD your God and rejoice, you and your household (Deut. 14:23-26).
When I was a teenager, a few buddies and I would periodically break into a local business. We used credit cards to jimmy the locks on the back door. There was no alarm. We would never steal anything of real value, but we always left with something little—maybe some food (ice cream or candy) or a pen—just enough to top off the experience. What experience? The exhilaration that attends such audacious mischief. For us to roam through the facility and not get caught was an adrenaline rush. We could do it. We did it. We were young, but we had the power. And we didn’t get caught. We were untouchable. We were like gods.
When Augustine was contemplating becoming a Christian Simplicianus, Ambrose's tudor and assistant, told him a story about Victorinus. Victorinus was a Roman rhetorician and translator of neo-Platonic philosophical works. He had begun to read the Scriptures and study the Christian faith, encouraged by Simplicianus. Simplicianus told Augustine that Victorinus once came to him in private saying, "I should like you to know that I am now a Christian." Simplicianus replied, "That I will not believe, and I shall not count you as a Christian until I see you in the church of Christ." That was wise advice from Simplicianus to Augustine, the young man for whom contemplation was everything.
The Latin in the title to this post means "There is no salvation outside of the church." Typically, we add "ordinarily" to that slogan just to be sure that everyone understands that there are extraordinary situations where people do trust Jesus but are not able to join with a local congregation. The point is, however, that becoming a Christian is not simply something that happens in your head.
Here's my short homily from Christmas Eve 2009. Every year during Advent and Christmas I spend some time reading Martin Luther's Advent and Christmas sermons. Anyone familiar with Luther's thoughts about the baby Jesus will recognize my dependence on him. Very few theologians have grasped the full significance of the incarnation of the eternal Son of God as Luther did. The true humility of God is unveiled in the story of Jesus' birth. God the Son united himself to our human flesh forever.