Christians: why do you celebrate christmas?

I am worshipping God; celebrating the birth of the Savior. I cannot "accidentally" worship a pagan god or anything like that unless I choose to. What does it matter what day we do it? By your standards, we couldn't do it any day of the week, since every single day of the week is named after a pagan deity. Christianity is not the same as myths. Christianity transcends, whereas the gods of pagan myths are elemental.