I believe those of Jewish faith still live by the 'old' laws because they don't believe that Jesus was the Messiah. Jesus coming as the Messiah brought the Mosaic Law to an end, so Christians aren't bound by the weekly Sabbath etc.

And it's very true that 'Christian' holidays are steeped in pagan tradition. Jesus birthday is unlikely to have been in December, it was all just combined with other pagan festivals held in December to become Christmas.