It's Advent, which traditionally has two focii.
The season is about preparing for the coming of Christ. The more obvious half of that is preparing to celebrate Christmas. The other side to it is about the final return of Christ to this world, when he comes to judge the living and the dead, to usher in the new heavens and the new earth, and to free the cosmos from its bondage to decay. What we, slightly mistakenly, call the "second coming". We remind ourselves that it's coming, and we prepare ourselves for it.