The secular world starts Christmas early--even before Thanksgiving nowadays--and ends it just as early. By the day after Christmas, regular programming resumes and Christmas carols are hard to find. Trees are thrown out on the curbside awaiting pickup.
But the Church's liturgy is just the opposite. Advent is a time of waiting and expectation. Once Christmas arrives, the liturgy celebrates the Christmas season. During these two to three weeks the Church offers us the opportunity to ponder the meaning of Christ's birth in peace and quiet.
The great thing about the liturgy is that it actually makes present the grace of the feast. It doesn't simply recall it, like we recall the signing of the Declaration of Independence on July 4. The liturgy brings us into a real contact with Christ and the grace of salvation that he offers.