As I have often written the month of January gets its name from the two-faced Roman god Janus. Janus had two faces with one looking back at the past and the other looking towards the future. This ability to see in both directions gives him a certain connection to thresholds such as doorways and windows. He has the rare gift of governing time. It seems that Janus is a very old member of the Roman pantheon of Roma gods and goddesses. It is possible that before Jupiter became such an important god of the Romans it was Janus who was the ore important deity. Even after Jupiter moved ahead in the ranks, yet Janus maintained his right to be first. As an important deity of beginnings, one soon to have a connection to the first day of the month with January 1st being his feast day.
When the Romans moved to new year from March 1st to January 1st, it became a day to honor the god of beginnings. With this ability to look back at the old year and at the same time look forward to the new helped make Janus a deity connected to divination, and rituals to start the new year on the proverbial right foot.
Homes were often decorated with evergreens such as holly and mistletoe with their obvious connection to magical forces. Decorating thresholds such as doorways were especially important to honor this lord of beginnings. His number one (obviously) and his tree is the sturdy oak. He sometimes goes by the name Dianus or Giano. And so, it goes.