There has to be a lot of truth in this statement referring as it does to the most popular of Christmas tales. The section which most evokes the spirit of Christmas is The Ghost of Christmas Present, in which Scrooge is shown a variety of people who know how to celebrate Christmas.
I find the spirit of Christmas is most strongly evoked and best defined in two of the less celebrated episodes, which both take place in particularly desolate settings. The first takes place on a bleak moor upon which the sun 'glared ... for an instant, like a sullen eye' before setting. This is the work place of miners where Nature, even the sun, brings no cheer. The only joy to be found is with the miner's family celebrating Christmas, singing and raising their voices above the wind outside their hut. Dickens is saying here that the Christmas spirit comes from within, within the human spirit.
The Ghost also takes Scrooge to see the sailors toiling on a sea every bit as bleak as the miners' moor. Dickens writes, 'every man among them hummed a Christmas tune, or had a Christmas thought... And every man on board, waking or sleeping, good or bad, had had a kinder word for another on that day than on any day in the year'. It is the idea that Christmas is something everyone can celebrate which Dickens also sees as the spirit of the time.
Additionally, one must consider the historical context in which Dickens wrote A Christmas Carol, during the Industrial Revolution, a time of rapid economic and social change in Britain. London was teeming with new factories and the people who wanted to work in them, which meant that it was also teeming with air pollution, unclean bodies, and disease. Child labor was a new way for a family to earn money, and Dickens saw the overall situation to be grim at best. The child labor issue was a particularly sore spot for him, as he had left school at age twelve to work in a blacking factory after his father, the big spender, was sent to prison for unpaid debts. Dickens saw this time in England as being one of greater and greater class division, the rich getting richer, the poor getting poorer, and A Christmas Carol explores these themes. Scrooge, the villain (at first) is the epitome of the money-hungry, unfeeling businessmen that Dickens sought to criticize, and his employee, Cratchit, is the epitome of the poor worker in England, supporting as best he can, a family. By depicting Scrooge as separated from Christmas, while his poor employee, Cratchit, as well as the sailors and miners mentioned above, are celebrating Christmas, Dickens connected the idea of a Christmas spirit as being apart and separate from money and resources, an idea that continues to this day.
Interestingly, while Dickens may have held magnanimous ideals about humankind, and a writer's talent for expressing them through fiction, his creativity and competence did not extend to money management, for his skills more nearly resembled those of his father. For example, with the publication of A Christmas Carol, Dickens took an enormous financial hit, insisting that the book be published with the finest coverings available, as well as high-quality typesetting and gilt-edged paper--while charging a fraction of what the book should have been sold for, because he wanted it to be accessible to everyone, rich and poor alike.