Final answer:
The diversity of early Jewish religious groups stems from differing interpretations of the Mosaic Law, the development and adherence to the Torah and Talmud, geographical displacement, and the influence of an egalitarian ethical system within Judaism.
Step-by-step explanation:
The extreme diversity of the first Jewish religious groups, who all believed they were following the Mosaic Law, can be attributed primarily to differing interpretations of the Mosaic Law. During the first century CE, the Jewish religious leadership was divided into different groups such as the Sadducees, the Pharisees, the Essenes, and the Zealots, each interpreting the laws of Moses and the practice of Judaism in distinct ways.
The Sadducees, for example, believed only priests needed to follow the detailed laws, while the Pharisees argued for adherence to all laws by all Jews, and other groups like the Essenes and Zealots took more ascetic or revolutionary approaches respectively.
Additionally, the development of Jewish customs and sacred texts such as the Torah and the Talmud arose from the need to preserve Jewish identity, particularly during periods of exile, allowing Judaism to be a 'mobile tradition'.
This adaptability was crucial in maintaining Jewish culture and religious practices despite geographical displacement and the eventual diaspora. The egalitarian ethical system proposed by Judaism, emphasizing the equality of all before God, also played a significant role in guiding the various interpretations and practices within Jewish religious groups.