The "Janus" figure is the Roman god Janus and his partner I think Diane but I am trying this from my memory of that Edith Hamilton book we had in high school. When I took the class, well it was probably "current events" instead of mythology 101. (oh ye gods and goddesses).Janus was a favorite of mine just because there was an image like the one here over the door to the auditorium. Fact is there is a likeness over the doors of most auditoria. Symbolically Janus had a lot to do with performance - the theater mostly - as when a play is put on, the audience enters into a new place where perhaps a new world is viewed or more sharply,the world of reality (the audience) and the world of make believe. Actors talk of an imaginary wall that separates the edge of the stage from the audience and you aren't to "break character" and 'play to the audience'. You stay on your side and they (the audience) views what you do.
Janus was considered the the god of doors. That seems odd but isn't. A door is a passageway ...on one side is the reality of where you are and on the other side, well, who knows. That is why the two heads; one looking back and one looking forward.
Christmas, for all the wild spending and ever increasing commercialism (what did Ferris Buellar say about "isms"?) is really the door way day of the year. We think of that as New Year's eve - out with the old and in with the new - and that would be the secular day. For those who believe in Christmas, this is the day. In a general sense we have BC and AD a big door that you enter at the Birth of Christ and leave thereafter at His death. But the timing is really when Christ the Child (Christ Kinderling, Kinderclaus, Kris Kringle of all things if you trace the words) is slapped on the bottom. Doorways aren't tunnels. They are little abstract force field vapor barriers instant transitions that take you from where you are to the future.
Perhaps we should think about Christmas as that. My last cat, Muggs, spent hours looking out the front door window. He didn't know what was out there (other than cold) and it scared him, but through that Christmas door is a new world and it is time to cross over and see it.