I like the fact that Christians 'keep score' and 'tell time' in another way besides the usual bottom line(s) of life and the mere chronology of the passing hours and days.
The Advent Calendar, part of 'the Christian Year' draws us into a time of yearning, longing, waiting - for the Fulfilment of the Promise that is Good News for this world. It's come and is yet coming just as Christ has already appeared (say, about 2,000 years ago) but also will come again at the end of the Age - to bring in the fulness of all that we have yet had only rumours and mere glimpses - some of us, anyway . . .
And still it's as if the whole house was in darkness, waiting for someone to turn on the lights - or Someone to enter Who is Light Himself !