Really? Hmmm... Celebrating the birth of Christ, my Savior. Okay, I got it. Doesn't seem very mysterious to me.
Sure it's taken over other holidays, but Christmas is about Christ. His birth, His life, our hope. Just like Easter is about a goddess, and the Day of the Resurrection is about Christ's triumph over death. Just like Halloween is about the day before the day about saints, and Samhain is about the new year.
To me Christmas is a remedy to the winter solstice and its darkness. It IS originally the pagan celebration of the winter solstice. The birth of Christ (possibly Jan 6 as celebrated in spain) was moved to absorb that holiday. Christmas is a welcome break in midwinter, with lots of light. I like the Indian concept: Diwali, festival of lights. In the Himalayas, and I suspect, other places in the world, the winter solstice is celebrated with parades of torch or candle bearers and bonfires. It's also the restart of the year. (I hope I didn't mix that up.) Using the lights and bonfires to lay waste to the bad things from the year past and start afresh. Not being religious, to me personally, Christmas is a yearly opportunity for family gathering, with a special effort in the cooking department, as well as decoration and perhaps dressing. My mother picks holly and pine branches and leafy branches, and spray paints some of that golden, and makes green and golden and red Christmas wreaths adorned with some of the Christmas decorations that usually belong on a tree. (Although the tree tradition is coming back for the grandkids.) She makes hollowed-out clay candle holders herself, lays them out around the dining-room... etc. Presents... are a chore. We don't need Christmas to exchange gifts. My dad's been on Christmas presents strike for a few years. (He hates weddings too.) He makes presents when he wants. At first I was for embarrassing him with presents (he gets them for Christmas all the same) but I kind of agree with him. His point is you buy something for a family member when you find it, and no need to wait until Christmas. Buying something whithout having an idea what, just to give a present, is a hassle and has less chances to be liked. Although whatever we do, our presents more often reflect our own taste than the recipient's.