In approximately AD 48, the Apostle Paul, his coworker Barnabas, and Barnabas’ cousin, John Mark, boarded a ship at Seleucia and headed for Cyprus to initiate their first missionary journey (Acts 13:4). It was during this mission that an unexpected setback occurred—John Mark departed from the mission shortly after their arrival at Perga in Pamphylia. Although Luke offers no direct reason for Mark’s departure, the events that soon unfold point to an unprecedented movement that occurs within the Gentile mission. This study examines the viability of the idea that John Mark's departure was potentially motivated by theological differences with Paul that the Gospel message could be offered to the Gentiles without the traditional requirements of Jewish proselytization. Additionally, this analysis addresses a possible theological rift which may have occurred between Mark and Paul, which happened somewhere between their departure from Paphos and their arrival at Perga in Pamphylia, where Paul may have shared his missionary objective to John Mark and Barnabas to evangelize to the Gentiles without the requirement of the adoption of the Mosaic laws in order to be saved. This question on the requirements for Gentile membership in the church and qualifications for Jewish-Gentile table fellowship would later become the central focus of the Jerusalem Council, and Luke may have intended for Mark’s departure from the first missionary journey to serve as the distinct event that initiated the Gentile question in the early church. Thus, John Mark’s departure from the first Pauline missionary journey may have been theologically motivated, based on his theological view that the Gentiles could not live sanctified lives apart from the adoption of the Mosaic Law. Further, it is proposed that this event both explains why John Mark returned to Jerusalem (and not Antioch) and why the Jerusalem council was convened immediately upon Paul and Barnabas’ return. As such, this event would spark controversy in the early church which was eventually resolved at the Jerusalem Council. Despite its apparent resolution, the effects of this event would be felt for several years, dividing both Barnabas and Mark from Paul’s continued missionary work. There is no indication that Paul and Barnabas ever worked together again, while John Mark would be divided from Paul for several years until they eventually reconciled. Through this lens, it would thus appear that Luke did not intend for John Mark’s departure to serve as a parenthetical note to his account, but rather as a springboard to one of the greatest theological challenges facing the early church in the evangelization of the Gentiles.