First of all let's just clear something up...Advent is not Christmas.
Advent is the four week season of anticipation of Christmas; much like Lent is to Easter. As Christians we do this because Christmas [and Easter] is a very profound event. We celebrate this because Christmas is not something that should ever sneak up on us. Now, if you're an American, I'm sure you're thinking, "Christmas...sneak up on us? They start playing Christmas music in Wal-Mart 3-4 months out!" My response is, "Do you think what they're celebrating is Christmas?" [more on that in the next post]
A common way of thinking about Advent is twilight [not the vampire movie...]. Much as twilight is the time just before daylight, Advent is the time, just before the Light of the world has come amongst us; just before God fully reveals himself to the world; just before God puts all his money on the table. Twilight is a funny time of day just BEFORE actual light.
Last year, I was a part of a group, and to celebrate Advent, we got up really early in the morning, sat in the middle of a field, and worshiped together in the twilight. This is what we do the four weeks before Christmas, we're coming together to worship in the twilight before the full light is upon us.
A friend of mine [who just so happens to be a pastor] recently announced to his church that they were not going to sing any Christmas songs in their church until Christmas. His reasoning: "Christmas music celebrates the coming of Jesus, Advent is the seasoning preparing for Christmas" - two very different things. Instead, the church is singing, "Oh Come, Oh Come Immanuel."
Oh Immanuel, God with us, please come!