Christmas is the most important holiday of the year. Especially since the 20th century on, the days adjacent to the holiday have become an occasion to do big business. The winter season is the most solid stimulus for the economy - more than any fiscal package - since the incomes of families, spending, credit, and consumption in all productive sectors are significantly increased. In the United States alone, Christmas sales are estimated to generate $3 trillion.

This jubilee of consumption and purchase of goods and gifts is accompanied by a series of child-pleasing customs: a pine tree with lights and ornaments inside the homes; Christmas carols; preparation of sweet meals and treats; the chubby figure of Santa Claus; and, to a lesser extent, nativity scenes depicting the birth of Jesus. Each country also preserves exclusive traditions that are highly esteemed among their own population. In Russia, people cook 12 dishes in honor of the 12 apostles, then return to the church for an all-night vigil. In Estonia, children must sing before receiving their gifts. In Mexico, groups of people wander from door to door singing the story of Joseph and Mary when they were searching for a place to stay, and inside the house that receives them, they break piñatas full of candy. In the United States, the streets are decorated with colorful lights, and choirs of children sing carols beside huge fir trees. In India, even with its Christian minority, people call Christmas "the big day" and celebrate it by planting trees.

The holiday animates debate, too. For those interested in history, it is the time of documentaries on television where so-called experts repeat the worn-out speech that the church deliberately put the date of Christmas over a pagan celebration, the Saturnalia, or Sol Invictus, the solar god of the Roman Empire. Others will say that Santa Claus is a legacy of Norse mythology related to Odin's journey through the heavens, and that the star of Bethlehem could have been a spectacular planetary conjunction that occurred in 7 BCE. For the self-denominated neo-atheists, it is the time to offer interviews on major networks and declare that everything is a hoax, and that the story of Jesus’s birth is a myth copied from the story of the god Mitra. The celebration goes unnoticed for no one, making Christmas arguably the only holiday that, for better or worse, unites the whole planet.

How did things progress from that story in the Bible, with a Jewish girl giving birth to the Messiah of Israel in a manager in the city of Bethlehem, to the modern colossus that is the Christmas holiday? How did Santa Claus, the Christmas tree, the snow sleighs, the presents, and family reunions become the distinctive features of the holiday if none of them were there at the beginning? The answers can be attributed to a chain of events, characters, oral traditions, artistic works, and an assimilation of local folklore.