My pastor tells us that Advent is the preparation time for the coming of Christ (the past and the future ones). We CELEBRATE Christmas AFTER the fact and not before. He tells us that for example, why celebrate a wedding before the bride and groom show up? (they could call off the wedding!

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Chrismtas is celebrated 40 days AFTER (and at that time, the secular world has put away ALL the trimings, tree and music).
Also, how would you explain where the Twelve Days OF Christmas comes from, the song is about AFTER Christmas.
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This is a very good point. I wouldn’t be surprised to learn that Christmas music starting in mid-November is part of the drive to get people shopping.
Having said that, I still like to start listening to it early. And it doesn’t affect our shopping habits, because we already have a decidedly non-commercial Christmas.
Another counterpoint is that there is a LOT of Christmas music that has been written, but there’s not much in the line of Advent music.