Right-o about Jesus fulfilling the Law and the Prophets. However, He directly went against the Jewish leaders of the day, and what Judaism is today as well. Jesus established new doctrines as well as affirming old ones. Christianity's doctrines are indeed based upon Jewish ones, but the differences are so large that Christianity could never be classified as a form of Judaism, in any respect.

For instance, Jesus is regarded as Messiah by mainstream Christianity, but not by Judaism. In mainstream Christianity, Jesus is worshiped as God, while in Judaism Jesus is labeled as a heretic.

Those are just two (very large) differences. How then could Christianity ever be classified as a Jewish sect? It's like a tree and a seed, the tree springs up from the seed, and is the direct result of the seed, but isn't the seed itself. (  )