By now you've probably heard why December 25th was chosen? According to the Roman calendar, 12/25 was the winter solstice, the shortest day of year, the longest night, the least light. But that meant it was also the harbringer of longer days, that the nights to follow wouldn't be as long. Thus this day took on festive (feasts and celebrations) of the victory of the sun over the conquests of the night. Apt metaphor in connection with the accomplishment of Christ on the cross.
All that to say, December 25th was a feast day for the birth of Christ, but for hundreds and hundreds and hundreds of years it was just another feast day and a day of worship, alongside all the other dozens and dozens and dozens of saints. Even with the feast day of Saint Nicholas on December 6th, there was no concept of gift giving as we know it, there was no traveling to spend time with family, there was no exchange of cards, no shopping for loved ones.
In fact, the one fact that made December such a wonderful time of the year was that the harvest was collected and it was the one time of the year when you slaughtered the cattle and pigs (it would keep a lot better during the winter...). December was the one month in the year when there was mounds of food to consume, it was a time of leisure for serfs and barons and farmers and slaves. The weather was usually mild enough to not prohibit public gatherings in the village, and it was thus a great time to make merry. Thus some fantastic feasts took place in December. Oh, did you know that December 26th is St. Stephen's Day? Just another day to feast!
But here is what is interesting about the feasts in December. Many of the peasants and serfs would "wassail" through the village to the homes of the rich(er), enter in, sit down at the table, and sing for some food. The "wassail" is our precursor to caroling throughout the neighborhood. But the "wassail" had much more of a dangerous edge: it was a song with a threat. If the "hosts" didn't provide the best cakes and ale in the house, the waissailers might have to get rough. As long as the hosts played along with a smile and generosity, everything stayed merry.
Why would the rich allow this sort of disgraceful intrusion, you ask. It seems it was one of the few times during the year when their was a flip-flop in the social order, when the peasants could tell the land-lords/barons what to do. And the rich allowed it as a way for the peasants to blow-off steam; a hard winter was on its way, and this little "game" of waissaling helped create some good-will.
This scenario led to an interesting development: during December it was expected that you would throw inhibitions out the window, and you would eat and drink as much as you could for as long as you could. It was also a time to make merry, blow off steam, be rowdy, harrass the rich and powerful, frolic and flirt. St. Nicholas Day and Christmas Day were just two days that happened to fall during this December decadence.
The Puritans opposed all this stuff for two reasons: first because the merry-making was tinged with gluttony and lust and drunkeness - too much unholiness! And the Puritans resisted the observation of Catholic feast days; and they led the charge in insisting that nobody knows the day of the birth of Christ (they argued that if God had wanted us to celebrate it, he would have told us when it happened).
In New England, as the Industrial Revolution increased the wealth and eased the hardships of many Bostonians, New Yorkers, Philadelphians and others, the season of December came under scrutiny. The working poor of the factories were demanding time off of work to feast, they were breaking into the homes of the patrician-wealthy to wassail for food, they were getting pregnant out of wedlock, getting stone-drunk, and putting whole cities in uproars with riots. The rich were getting tired of the December decadence. It was time to do something about it.
The result: Instead of the rich focusing on the poor - giving gifts of food and drink, they created a Christmas where adults give gifts of books and simple toys to children. Instead of public festivities that the working poor often turned into riots, a Christmas was created where families spend time together at home in a quiet dinner. Instead of encouraging the decadence of the working poor in December - their gluttony and carousing and ribald waissaling, a Christmas was created where people over-indulged in commercial exchanges, going overboard in their special gifts to children and women.
If you find any of this interesting, be sure to visit your local library and read The Battle for Christmas by historian Stephen Nissenbaum. A fascinating insight into the development of our society - the powerful forces that shaped our concept of the family, of the holidays, of the relationships between the rich and poor, the fusion of civic duty and commercial-capitalism, the tension between religion and pagan festivities.