That's a sneaky one. Most never think to even check it, probably because it's not one fixed day like the others. But it, too, is a pagan holy day. Look into why we give gifts to the birthday boy, sing to him, and he blows out candles.
Candles, btw, especially those that, if you think about them, you can't figure out why they are in the tradition, are a tip-off that there may have been some witchcraft origins to the party. More than likely, if you start asking "why", you're going to find out why about the candles and a lot more.
@leastofthese There are many other remnants of witchcraft and paganism in our society. They're in plain sight, but they are disguised by centuries of alteration and down-play. We are so accustomed to them that mostly we never think about them. For instance, the children's rhyme that begins "eeny meeny miny moe" is a derivation of an incantation that proceeded lot-casting.
A lot of people don't want to hear this stuff, and when they do they would rather not believe it. I agree with
@raulus that we are not to fear it or really even consider it to be significant. I think what Paul was saying was that, as children of God, being freed from those chains to darkness, we now have license to look on those things with indifference. They can't hurt us anymore because we don't belong to them. "Where oh death is thy sting?" And, "greater is He that is in you than he that is in the world." If you've ever encountered deeply superstitious people, then you know what true fear of these things looks like.
On the other hand, if you find that you can't research these things without feeling uncomfortable, or if someone even mentioning them causes you to feel anger or fear, then my advice is to both stop and pray, because that would be a sure indicator that your faith is weak, and you might also be hiding idols in your heart. It's not for anyone to know everything, and only you know if it is the Lord who is telling you to look into these things or not. And only He knows why.
For myself, it started out as a curiosity about things that I couldn't explain, but now it has become a seek-and-destroy mission for anything false that's been planted in my mind. This applies to things of the world as well as things of the Word (edit to clarify: man's interpretation of the Word). I hate lies.
Even if you don't actively seek things to question, eventually in your walk with the Lord, you ought to get to the point where, even if you're not doing it regularly, you
can ask "why" (and not shrink when others ask "why") about
anything with boldness and not fear. The more you do it, the more you'll find out that people can make an idol out of anything, even Bible verses, and asking "why" tends to threaten to topple those idols. The topic of holidays isn't a bad way to build that muscle.