christmachrist
Explanation
The Joke
A preacher-like figure addresses his congregation, announcing that since people say there is not enough Christ in Christmas, he is introducing a new holiday: "Christmachrist!" -- essentially doubling down on the Christ component. He anticipates that "weak-hearted, so-called Christians" will say that "maybe Christmas is enough" or "stop yelling outside the library." He argues that this country was "founded on Christian Christmas Christian values" and Jesus would have wanted his concerns reflected. Someone tells him to get out of the church, and he cheerfully responds "And have a Christy Christmachristmas!" The bonus panel shows the comic creator actually made a Christmachrist card.
The Humor
The comic satirizes the annual "War on Christmas" discourse where some commentators insist that Christmas has become too secular and needs more Christ. The comic takes this complaint to its absurd logical extreme: if one serving of Christ in Christmas is not enough, why not just keep adding more? The result is the nonsensical portmanteau "Christmachrist" and the even more ridiculous "Christy Christmachristmas."
The character exhibits several traits that undermine his own argument: he is yelling outside a library, he gets kicked out of a church, and his rhetoric about the country being "founded on Christian Christmas Christian values" devolves into self-parodying word salad. He is so aggressively Christian that even actual Christians and churches want nothing to do with him, which highlights the irony that the loudest voices in culture-war Christianity often alienate the very religious communities they claim to represent.
References
The comic references the recurring American cultural debate known as the "War on Christmas," popularized in the mid-2000s by conservative commentators who argued that phrases like "Happy Holidays" were attempts to remove Christianity from public life. The bonus panel noting "P.S. Yeah, we actually did this" suggests that Zach Weinersmith actually produced physical Christmachrist cards.