Stephen Law has a nice post that highlights the value of community rituals and traditions. He concludes:
Christmas is a celebration of peace and love, and a time to think of others, especially those less fortunate. It is a time at which we come together, at which we feel solidarity and empathy with the rest of humanity. But of course these are values and aspirations that can be shared by non-Christians too. Much of the true meaning of Christmas is open to everyone, whatever their religious beliefs.
I'm suspicious of the idea that there's any one "true meaning" for a cultural tradition like Christmas. It's presumably going to mean different things to different people, and I don't see that anyone has the authority to impose their preferred conception on anyone else. Cultural significance and shared meaning are socially constructed in the strongest sense: it's up to us to make of them what we will. If you imbue the holiday with great religious significance, that's fine. If you don't -- if you just cherish the opportunity to spend time with loved ones, and to participate in tree-decoration, gift-giving, and other fun rituals passed along through the generations -- that's fine too. The meaning(s) of Christmas emerge, bottom-up, from how we choose to conceive of it. To think otherwise is the same fallacy as thinking that dictionaries fix what words mean (and don't get me started on grammar rulebooks!). There is no such top-down authority. "Prescriptivists" might like to boss others around, but we're not obliged to listen to the petty authoritarians.
I leave you with the greatest Xmas song ever:
Have yourself a merry merry Christmas
Have yourself a good time
But remember the kids who got nothin'
While you're drinkin' down your wine
And remember, you can still join the UNICEF Facebook Chain, here.