I don't mean the feast of Christmas proper,
Verbum caro factum est, the decree that went out from Caesar Augustus, and all that. Theologically, it's about as fixed as anything in the Enchiridion, and liturgically it's all over the map these days.
I mean the general cultural celebration of Christmas.
It's been well-documented how it's changed before. If we take the late mediaeval period as a baseline -- it's arbitrary, but relatively well documented, unlike, say, a sixth-century baseline -- and our domain the English-speaking world, then we can enumerate at
least the following stages:
1) The late mediaeval period has a somewhat merged public/private set of "secular" observances of Christmas. It's where the limited set of real carols comes from (they were the music for country dances, not for singing in church), where the "feast of misrule" traits which survive into Shakespeare come from, where the "unruly"
public customs of wassailing, mumming, and so forth come from. Public observances at a high level were a mix of the stately (the holding of a Christmas Court) and the liturgical (elaborate Christmas masses in the presence of the monarch). (It's at the very end of this period that Martin Luther invents the Christmas tree off in the Holy Roman Empire; it takes four centuries to reach England, although a little less to reach Canada.)
2) The Elizabethan settlement (skipping over the wild swings of observance under Edward and Mary) preserved (or at least did not very heavily suppress) much of the low-level popular observance, especially as many of the magistrates might be nostalgic for the old days themselves (things might vary widely according to the views of the local squire). It did, however, cut down on the explicitly religious side (no more midnight mass, and the monarch, now head of the church, no longer required the validation of the liturgy in quite the same way). I'll treat this as covering the general patterns of the Jacobean and Caroline periods as well. Old customs and beliefs were already becoming of "antiquarian" interest.
3) The Commonwealth suppressed Christmas, not very successfully.
4) The Restoration and Eighteenth Century brought Christmas back, but the social changes which followed the Revolution of 1688 gradually made many of the local observances still more "antiquarian", and the dislocation of the Commonwealth probably caused many customs to fall into desuetude in any case.
This is usually considered the low point both of Christmas observance (between the Renaissance and the Victorian revival) and of religiousness in the (rather Erastian) Church of England. Nevertheless, there are evidences of surviving customs even in an urban setting --
I am a young woman and have my fortune to make for which reason I come constantly to church to hear divine service, and make conquests: But one great hindrance in this my design, is that our clerk, who was once a gardener, has this Christmas so over-deckt the church with greens, that he has quite spoilt my prospect, insomuch that I have scarce seen the young baronet I dress at these three weeks, though we have both been very constant at our devotions, and do not sit above three pews off. The church, as it is now equipt, looks more like a green-house than a place of worship: the middle isle is a very pretty shady walk, and the pews look like so many arbours of each side of it. The pulpit itself has such clusters of ivy, holly, and rosemary about it, that a light fellow in our pew took occasion to say, that the congregation heard the word out of a bush, like Moses. Sir Anthony Love's pew in particular is so well hedged, that all my batteries have no effect. I am obliged to shoot at random among the boughs, without taking any manner of aim. Mr. SPECTATOR, unless you will give orders for removing these greens, I shall grow a very awkward creature at church, and soon have little else to do there but say my prayers. [from The Spectator]
-- (greenery as a mark of the season has a very long lineage, much antedating the English adoption of the German Christmas tree).
5) The Victorian period is marked by a firm attempt to suppress the surviving rowdy observances of Christmas while reviving in a domestic setting antiquarian customs. Christmas carols come back in (stripped of the drunken revels of a wassailing party), reaching their height in the early 20th Century with Dearmer's
Oxford Book of Carols. The plum pudding, which had a general association with festival in its origin, becomes firmly tied to Christmas observance, as does its cousin the fruitcake. The Victorians were the inventors of Christmas cards. Christmas trees came over with Prince Albert. Off in New York, many of the critical factors merged to create the Christmas figure of Santa Claus, as a blend of the English Father Christmas and the Dutch variant of St. Nicholas (who was a December 6th figure). Christmas presents also seem to have emerged from the oranges, nuts (or coal) associated with St. Nicholas.
In many ways, when I was growing up, we still lived (or so it seems to me) in an aftermath of the Victorian stage. The principal innovations had been electric Christmas lights, which meant that a Christmas tree could be lit up for more than a few hours on Christmas Eve / Christmas Day (when it was green and reasonably safe to use lighted candles).
Commercialism was nothing new, either. The Christmas card was commercial from the beginning.
By 1954, C.S. Lewis was already complaining about a commercialized Christmas which had much the same shape as the one we have now (in his "Xmas and Christmas: A Lost Chapter from Herodotus").
I wonder, however, how much the Victorian pattern is attenuating and being replaced by a newer one. It can be hard to tell: one's own experience of domestic Christmas is likely to be fairly stable, but what may have been "normal" for your family forty years ago might be rather rarer now; so what one perceives as a relatively little changing pattern could be in rather greater flux. (It's like one's own idiolect. One starts out with a baseline set domestically, modified by one's own early peers, but as one gets older, it will diverge from what younger users of the language have as their idiolects.) I've had basically the same pattern of observing Christmas since the early 1980s, and I go to a family Christmas Day gathering which has been ongoing since before I was born.
Certainly, in central Canada, it seems to me that there is a very much reduced importance of Christmas cards (which bulk large in Lewis' description, and in my own memory), compared to when I was young, and that this antedated the emergence of e-mail. (Part of the local reason for this may have been the postal strike of 1975, ending December 2, which disrupted many people's habits of organizing and sending Christmas cards early.)
Certainly, too, the increased secularism of the Canadian context has led to the replacement of carol singing assemblies in schools (using sheets produced by the local papers) by winter pageants with generic winter themes. (The decoupling of what one might call broadly a "festival of lights" decoration period (running from early November to early January) from any specific religious associations has probably assisted, not discouraged, the extension of generic festive decorations in public spaces.)
Environmental concerns have led to the abandonment of actual Christmas trees in many (but not all) public contexts for more abstract light decorations. The cheapness (both as an initial outlay and as a running cost due to low wattage) of LED Christmas lights have encouraged a proliferation of light-oriented decorations.
Christmas cake seems to be present mainly by it's absence, with snarky comments being made about regifting it or using it as a brick. Making a pudding is a time-intensive process which requires thinking some weeks ahead; I doubt that it really survives except among Anglophile foodies.
The commercial impress of the general decorate-and-give-children-presents (and, the merchants would like you to remember, other adults, including yourself) meme is unlikely to go away given its rootedness in the mercantile profitability model; the people who replace gift-giving by charitable donations, or who insist on holding to giving only handmade presents to close family, are probably going to remain in the minority, and immigrants are likely to pick up the pattern (via pressure from their children via their children's peers) unless they have specific cultural reasons for resisting it. (Even then, Hanukkah, for example, has come to resemble general North American Christmas a lot more than it did a century ago.)
The downtime pattern of the mid-20th Century (and the Victorian period), whereby things basically stopped for a couple of days, still holds on in England, but in North America it has been displaced by the Boxing Day sale, with a hectic week following Christmas.
But I wonder, though, how much the "reunite extended family" pattern is likely to be taken up by immigrants from other cultures who aren't inclined that way in the first place, or for whom it's impractical.
At what point can we really say that we've moved into a different mode of winter festival celebration than that which the Victorians left us? I don't think that it was true fifty years ago; but I am beginning to suspect that it is beginning to be true today