As for the official view of Urianism -- I will say unto you, feel free to take it or leave it.
We are not Christians, but we do acknowledge that Jesus/Yeshua was a real human being and delivered a legitimate message, and literally rose from the dead and transcended to heaven. We view Jesus as the primary human face of the Christ Spirit, Immanuel (God With Us), which is to say, ultimately, a human face for the Divine Will/Word.
We worship The One, but we are not opposed to sincere Christianity, neither to those Urians who prefer to focus on this human face for The Deity.
Moreover, none know when Jesus was born exactly, so the 25th of December is as good a time as any.
Furthermore, those who say it's just the pagan Saturnalia, a day dedicated unto Saturn (Chronos) -- our answer would be, whatever. Saturn/Cronos is another ancient aspect of the Supreme Being in our view (like An/Anu, Uranus, Aten, etc).
In regards to the tree and ornaments and lights: for a Urian these might best reflect the idea of the Tree of Life, and indeed, of the ladder of being (the angel/star at the top).
In regards to its meaning for us, we can be happy that Jesus/Yeshua existed (exists), that he lived, taught, died, and rose... he is the primary example of ascendance, the divine man, homo-angelicus, the conqueror of the grave and of reincarnation. He is an exemplar, at least of what we call the Right Pillar. He is indeed mediator, as asking him for assistance in overcoming sinful desires, I can testify, works very well. Indeed, he is a personification of divine grace -- and we all need grace.
More than this, Christmas for us should be held as a time to celebrate giving, charity, family, and love itself (Divine Love - Agape), and as a time to redouble our efforts to express kindness and compassion.
I don't celebrate it myself, but don't oppose it... My wife loved it, and Uriel had no issue with that. Uriel loves Jesus/Yeshua, respecting The Christ Archetype and Personage as a face and emanation of The One. And indeed, Christ is an archetype of sonship and the divine hero, overcoming the darkness of death and hell.
In the sense of Saturnalia, or Misrule, it was a time to vent all that pent up stuff and the dream of the return of the Golden Age, when heaven and earth were united; and as such it was an exercise in integrating The Shadow within us all, through innocent fun and ruckus celebration.
I would say, that I would hate to see Urians as a whole become a bunch of rigidly uptight puritanical sorts -- as our goal is integration and wholeness, moderation and balance. So have fun, though perhaps keep it family friendly... laugh, sing, dance, imbibe and feast... most of all, be huggy and loving toward each other, mend fences, rebuild bridges, make peace with yourself and others, and reach out to help those who are least fortunate and most downtrodden.
Anyway, that's my take on it. Don't over think Christmas, and other such holidays -- not with so many truly weighty and serious issues that need to be faced, both within ourselves and in the world around us.
Peace Be Unto You All
& MERRY CHRISTMAS (A Happy New Year)