A sweater in one hand, a pair of slippers in the other. The cashier is fast, but the surge in a line of Christmas shoppers is faster. Suddenly, your elbows crush into some ribs, not yours. You stare ahead, kicking yourself for not starting your Christmas shopping sooner. You think: Why did I fall for this sale?

As you angle toward the cashier, you wonder how the birth of a baby in Bethlehem has come down to the busiest shopping season of the year. Maybe you remember the time when people regularly prayed and fasted and did works of mercy during Advent in preparation for the birth of Christ. Day after day, coupons clutter your counters, newspapers track how much you buy, and your dreams are subverted by maneuvers in mall parking lots.

You may not have thought of this, but enduring the traffic, crowds and unresponsive salespeople during the Christmas season requires patience, or patior - Latin for suffering. Shopping at Christmas is merely this ancient concept's contemporary form.

This is the theory, at least, advanced in a book whose title you might have spotted among this season's new releases: I Want That! How We All Became Shoppers (HarperCollins, $24.95).

"The gusto with which people compete to tell the most harrowing holiday shopping story demonstrates that the sacrifice of shopping is an essential part of the ultimate celebration," author and cultural critic Thomas Hine writes of the Christmas season. These horror stories prevail even though people clearly enjoy the lights and decorations, the music and the crowds.

If you dared leave your space in line to find a bookstore, Hine wouldn't be there to take your questions. The Christmas rush has prevented him from signing books at local stores - it interferes with shoppers, the bookstores tell him - but as you wait, you may want to hear what he says by phone from Philadelphia.

He has thought about your situation carefully; ever since he saw people sink millions of dollars into the Internet to try to change the way you shop, only to lose it, he has wondered why you shop.

Unlike other authors on shopping, he is not going to scold you for it. Shopping is good. "It's about things that are very important to us as a species and as a culture," he says. "It's not trivial."

Some people even treat it like sex. They giggled when Hine told them what he was researching. And the truth is, he says, shopping has a lot in common with sex. Just about everybody does it, and most people worry a little bit if they're doing it right. Both provide the opportunity to make foolish choices.

After studying the way people have shopped at ancient markets all the way through our present-day habits at malls, on the Internet and in catalogs, Hine has his theories - the first being that shopping makes you feel powerful. Shopping, whether at Target or Neiman-Marcus, is also a form of exercising freedom. What else explains the fact that after the Taliban was deposed in Afghanistan, everybody went shopping?

There are higher expressions of exercising freedom, Hine agrees, but shopping is universal; in an industrial society, the possibility to exercise it is available every day.

Why is this good? It gives people a feeling of power over their lives. Shopping gives people the freedom to create themselves. It is no longer possible to tell a person's social status by his clothes. The enemy of shopping is the idea that people hold fixed roles in society.

Hine has found other motivations for shopping: People shop out of responsibility - for example, women who bring home basics as well as luxuries to nurture their families - or to seek attention, to discover new things, to feel like they belong.

But let's return to the Christmas rush. Even Hine admits that the stress associated with Christmas shopping is over the top. What you may not know, he says, is that it was meant to be stressful. It is part of the preparation we require to make the holiday meaningful.

Long before Christmas, there was gift-giving. What Christmas forces us to do, Hine says, is to decide who the really important people in our lives are and not only provide a measure of their importance with how much we spend on them, but also make a "judgment about their individuality" and pick out something that is going to enhance it. This is far more difficult than picking out something for yourself, he notes.

"To me the hardest part of Christmas is friends and relatives you don't see very often, or a change, especially in kids, you don't understand. There is nothing worse than giving the wrong gift to a 12-year-old - and in my experience, you almost always do."

Now maybe you're thinking, what about our cultural anxiety this time of year? The panic of retailers, the fear parents have of disappointing their children, the worry that the creche again will be swallowed up in wrapping paper.

Don't blame the retailers. If they could do it over, Hine says, they would hardly invent a system in which so much of their business depends on such a small part of the year.

You may be surprised to learn, as Hine was, that retailers resisted Christmas at first. In the beginning of the 19th century, gifts were purchased in one day, on Christmas itself, a fact Hine discovered when he unearthed an 1850s drawing in Harper's Weekly showing people crowding Chestnut Street in Philadelphia to buy presents on Christmas morning.

Store owners disliked depending on one day to bring in most of their sales for the year. It was difficult to store so many goods on the shelves, too. One of the first things they did, Hine says, was to try to extend the Christmas season in the hope of avoiding the crowds in the few days before Christmas. (Newspapers joined them in the idea, since they benefited from advertising.)

Until he wrote this book, Hine had no idea of the strong connection between the growth of the commercial Christmas and the religious one; there in Philadelphia, John Wanamaker, the department store owner, published and freely distributed one of the first books of Christmas carols, helping to make them popular.

Both the religious Christmas and the commercial one "are a reaction to a kind of desire for a holiday celebration for the family, and the mother and beloved children," Hine says.

The people who made Christmas - still do - are women. And now, as you reach the cashier, goods in hand, you begin to wonder: Would Aunt Sally look better in the red sweater or the black one?