Happy Janus day 1, in the New Year of 2019 AD or CE as you prefer.
January is, of course, named after that Roman demigod Janus, the ruler of beginnings and endings. Humans have a way of discarding old gods while still letting them direct our lives, and Janus is a good example of that. Much of what we call “tradition” is really “old god belief” that we had to rename in order to keep practicing that religion, in this case with our New Year’s Eve celebrations. Our recent observance of Christmas is another example of this practice, with many of our most defended traditions, for instance, the December 25th date and the Christmas tree, having “pagan” roots. 
The Anno Domini (“year of our Lord”) dating system did not come into existence until 525, and took some two hundred years after that to catch on (and “year 1” was likely inaccurately calculated at that). Even that “God language” of “AD” and “BC” is gradually phasing out as the “Common Era” usage of “CE” and “BCE” becomes much more, er, common in academic and popular writing. The “God language” fades, but the dating system remains. 
Naming the months and days
The “theology” of old religious celebrations like the New Year is so deeply embedded in culture that it ceases to be recognized as theology. There is nothing cosmologically significant about the date because there is no “marker in the sky” that tells us this is exactly where we were last year at this time. The Sun is moving through space-time at about 43,000 miles per hour (70,000 km/hr) even while the Earth revolves in a vortex motion around it, and so we would have left that marker some 377 million miles back by my calculation. 
Other remaining month names also have their origin in Roman and Greek deities (March and May), religious rituals (February is derived from a Roman purification rite) or Roman rulers who were elevated to divine status (July and August, stealing days from poor February). Mercury, Venus, Mars, Jupiter, Saturn, Neptune and Pluto enshrine the Roman pantheon of gods in the night sky. As the exception, our own Earth has its name rooted in a Germanic goddess.
The majority of English names for the days of the week pay homage to Norse and Germanic gods (Tuesday, Wednesday, Thursday and Friday) , while the even-earlier worship of the Sun and Moon identifies two more days. The Romans sneak in another demigod on Saturday. These deities all remain ubiquitous in our culture even as we claim no supernatural belief in them. Noted atheist Richard Dawkins points out that, “We are all atheists about most of the gods that societies have ever believed in.”
The dusty pages unread
Christianity itself has, over many centuries, largely relegated the harsh Old Testament Jehovah/Yahweh to secondary status in practice, if not officially. Many Old Testament books have unofficially been “de-canonized” through disuse, its “God language” no longer relevant enough to preserve except through the cheap printing of unread pages. This is mostly a good thing. Even the most fundamentalist preachers typically only quote a tiny sliver of Leviticus from the pulpit to condemn homosexuality, tactfully ignoring all of the other “abominations” more likely to apply to many others in the pews. 
The expanded Mosaic Law detailed in Deuteronomy and Leviticus is mostly ignored by Christians. Some insist on posting the Ten Commandments from Exodus chapter 20 in courthouses, yet few could likely recount them if pressed.  Some of the prophetic books (e.g., Haggai and Obadiah) are so little read that only a handful of scholars can quote them. Handel’s oratorio Messiah preserves in popular culture only a small portion of the book of Isaiah. The Song of Solomon is very racy when read literally, so it is one of the few Biblical books that Christian fundamentalists insist on reading as allegory. While most Christians would still place the Old Testament Yahweh/Jehovah as “top dog” in the Trinity “godhead,” they clearly spend less time talking about him.
Even from the New Testament, most Christians can’t even agree on a pronunciation for the book of Philemon, let alone quote from it. Most Christians haven’t figured out that the second person in the “Trinity godhead,” Jesus Christ, is presented quite differently among the four Gospels, very human in the earliest gospel, Mark and almost completely divine in John, emerging several decades later. Many Christians commonly assert that the Bible is “divinely inspired and inerrant” in its entirety, despite mostly not knowing what is in it.
Some Christian ethic has installed itself deeply in culture. Traditional Lutheran values on how to treat other people, especially the poor, seem to still reign in Scandinavia despite some of the lowest percentages of formal religious practice in the developed world. But on the other hand, many American Christians ignore Matthew’s story of the Baby Jesus spending his early years as a refugee in a foreign land, fleeing a very severe “family separation policy.” Some religious tradition is so embedded in the individual psyche that it looks genetic, and indeed it may be. And yet sometimes the best parts just don’t seem to “take” very well at all.
At any rate, today we celebrate the first day of the month of the god Janus. May you have a good “new beginning” whether you believe in Janus or not.
By the way, here is a cool simulation of how the Sun moves through space-time, and how Earth and the planets then move around the Sun in a vortex motion. As a departed friend once told me, “If God is real, then the more you learn about reality, the more you learn about God.” Here is the reality – billions of galaxies consisting of many more billions of stars and even more billions of planets, zooming through space-time over the past 13.799±0.021 billion years:
- The word “pagan” and our common use of the lowercase g has been our method of subtly dismissing gods past so as not to offend “God present.”
- The term “Common Era” as an alternative to Anno Domini, despite its more recent trend of acceptance, has roots going back to the 1600s. And computer scientists still bemoan the lack of a “Year Zero” since the systems both go from 1 BC to AD 1.
- Fraknoi, Andrew. “How Fast Are You Moving When You Are Sitting Still?” Astronomical Society of the Pacific, 2007.
- Tiw, Woden, Thor and Frigg, respectively.
- There are, by my count, fourteen uses of the word “abomination” in the King James Version of the book of Leviticus alone, out of some 136 in the total Old Testament.
- Quick: Can you name them? See my take on “The Ten-ish Commandments.”