In 2006, I was attending several week-long classes at the Spertus Institute for Jewish Learning and Leadership in Chicago. One of the classes was titled "Who is a Jew?" and was taught by my doctoral advisor, Rabbi Dr. Byron Sherwin, of blessed memory. The course discussed biblical, rabbinic, medieval, and modern perspectives on the question. As Rabbi Sherwin was accustomed to doing, he typically included unusual cases for us to consider. Decades before, a student at the Spertus Institute had stirred some controversy. According to Rabbi Sherwin, the person had been an exemplary student. He excelled in all his course material. There was one issue, however. Unbeknownst to his fellow students or teachers, the student was the leader of a Messianic Jewish congregation in the Chicago area. He graduated, if I remember correctly, with a bachelor's degree in Jewish studies. The student it appears was not trying to stir controversy at the school nor was he actively engaged in evangelistic endeavors. Someone, however, had recognized his name and sent the information to the Spertus administration. Significant donors were upset and contacted Rabbi Sherwin. Rabbi Sherwin invited the former student to sit down and talk about the controversy. The student told the history of his eastern European Jewish family. During the Second World War, the family had converted to Christianity and as a consequence had been helped by other Christians to escape. The student explained to Rabbi Sherwin that Jesus had saved his family, literally. Rabbi Sherwin was speechless. Rabbi Sherwin asked us if the student was Jewish.The story was one of many that were discussed in that class and which caused us to consider the multi-faceted nature of Jewish identity in modernity. This is-sue is almost always an emotionally charged topic. The typical response to the scenario mentioned above is fairly consistent by most mainstream Jewish institutions. The changing nature of the American Jewish community and the intermarriage rate, however, are altering long-held perspectives and creating controversy in an area of Jewish thought that was once uniform. This short work is intended to review two extreme cases of this phenomenon. The introductory chapter presents the case of Cardinal Jean-Lustinger and a hypothetical question asked by Rabbi Sherwin. The second chapter focuses on the topic of heresy and apostasy in Jewish thought. The third chapter delves further into the question of apostasy introducing the idea of limited apostasy. The fourth chapter discusses the status of Jewish converts to Christianity. The last chapter discusses perhaps the most perplexing case of all, that of a Jesus believing Orthodox rabbi and the unexpected challenges such a scenario presents.