This question really isn’t the issue. The question “How can you be Jewish and believe in Jesus?” is better answered with another question: “who is Jesus?”
If Jesus, as claimed, is Israel’s promised Messiah, then according to the Scriptures, in order to be a truly observant Jew one must acknowledge and believe in Jesus as the Messiah.
One is either Jewish or Gentile by birth–nothing can change that. According to the Bible, a Jew is a person who is descended from Abraham, Isaac, and Jacob.
Jesus and His earliest followers were Jewish. They never renounced their Jewish heritage. Nor were they expected to do so. Believing in and trusting the Jewish Messiah can add to one’s appreciation of Judaism.
Author: Dr. Michael Brown, as published in Sid Roth’s book, There Must Be Something More! (Brunswick, GA: Messianic Vision Press, 1994; Kindle Edition ©2009). Used by permission.