Jesus was Jewish and so were his disciples. He did not start a new religion, but his movement was consistent with being one of several sects of first-century Judaism.
There were probably essentially very few non-Jewish followers of “The Way” (Jesus, Yeshua) for the first ten years or so after his death and resurrection. Paul was Jewish and never stopped being Jewish as evidenced by his willingness to pay the temple fee at the completion of the vows of some individuals as mentioned in Acts to show that he had not become apostate. However, he was a strong advocate for not forcing the non-Jews to convert to Judaism by being circumcised and observing all the kosher rules before being allowed to be accepted as a follower of Jesus. In fact, the matter was definitively decided by the Jerusalem Council when they ruled in favor of Paul and Barnabas (and against James) in that all that would be required of non-Jews who wished to follow Jesus was to observe the “Laws of Noah” which related to practices associated with immorality and idol worship.
While we non-Jews are not required to observe the biblical feasts, etc., we are certainly not forbidden to do so either. Not only do many non-Jewish followers of Jesus find the experiences very meaningful, it often illuminates scripture in a fresh new way and promotes a fuller understanding of biblical events and teaching. It is tragic that by making “Christianity” the official state religion and making “Jewish” practices illegal for Christians, Constantine essentially finalized a rift that had been developing between the followers of Jesus (both of Jewish and non-Jewish origin) and the Jewish people who had chosen not to follow Jesus since the first century.
One of the problems Christians have is with the biblical term usually translated in English as “law.” The same word in the Bible, however, is translated as instruction, precepts, etc., which evoke very different emotional responses. “Law” makes us think of something forced upon us and the penalty we may expect for violating it. On the other hand, “instruction” and “precepts” are much friendlier terms and evoke feelings of helpfulness and guidance as a loving parent instructs his or her child in proper behavior for the child’s benefit—yet it is the same Hebrew word.
What was making Paul so angry was that members of the James party were telling Paul’s converts to Jesus that they weren’t real followers of Jesus since they hadn’t been circumcised. That’s why he angrily lashed out and wished that they would “go castrate themselves.” While not exactly the same, we have seen people who become so enamored with “Jewish Roots” or “Hebrew Roots” (often, primarily with the externals) that they somehow feel that following these practices lifts them to a higher position with God. It’s almost like the Gnostics who believed that their “secret knowledge” gave them special favor with God. [Please don’t think I am referring to you in this matter—I suspect you yourself have encountered individuals like this.]
Paul was certainly not against celebrating the feasts as evidenced by the fact that he made a great effort to be back in Jerusalem in time for Passover. He just didn’t want the non-Jewish followers of Jesus to be forced to keep the feasts and other rules of Judaism, but neither did he forbid those who wished to do so.
While I do not believe non-Jewish Christians are required to observe Passover, I believe it will be an eye-opening experience if they do attend at least one Seder conducted by a follower of Jesus. One of the cornerstones of our faith was instituted by Jesus during the Passover meal—the memorial to himself—Communion or the Lord’s Supper. The events of the Bible, including the New Testament, did not happen in a vacuum. I believe that while the practice of Jewish feasts and customs is not required of non-Jewish followers of Jesus, an understanding of Jewish custom and practice will enhance the understanding and deepen the faith of any individual. And what serious follower of Jesus would oppose better understanding Jesus and his teachings?