On this day in 1843, A Christmas Carol by English author Charles Dickens was first published (first edition pictured below), arguably influencing Christmas as we know it more than any pagan tradition. In fact, the phrase “Merry Christmas” was popularized by the story!

Dickens was ambiguous about religion; while he was likely a Christian and admired Jesus, he openly disliked rigid orthodoxy, evangelicalism, and organized religion. (He once published a pamphlet opposing the banning of games on the Sabbath, arguing that people had a right to pleasure.)
To that end, a Christmas Carol placed less emphasis on faith and observance and instead focused on family, goodwill, compassion, and joy. Dickens sought to incorporate his more humanist approach to the holiday, constructing Christmas as a family-centered festival that promotes generosity, feasting, and social cohesion. Some scholars have even termed this “Carol Philosophy”.
So when religious and nonreligious folks alike think of loved ones and the “Christmas spirit”, they are basically channeling Dickens’ once-unique take on the holiday. (Though in his time, other British writers had begun to reimagine Christmas as a celebratory holiday, rather than a strictly religious occasion.)