2006 years ago Jesus Christ was born, according to Orthodoxy. In Russia people usually celebrate Orthodox Christmas, which is on January 7 unlike Catholic Christmas, which is on December 25.
In Russia it is more of a religious holiday than regular national holiday. This is partly due to the fact that Ded Moroz (Father Frost) with all the presents come on New Year, and all the celebrations actually happen on the New Year too, so there is not much left for Christmas, except for church services.
There were no gods in the USSR, and no religion too, and people didn’t celebrate Christmas as they do now until very recently. So one can call it a relatively new holiday.