Although the Torah is wonderfully rich in its narratives, poetry, and laws, it is inadequate as a law code. For example, Deuteronomy decrees that if a man divorces his wife and she remarries and the second marriage ends in divorce or death of the husband, the first husband is forbidden to remarry her (24:1-4), but nowhere does the Torah clearly define how the divorce is to be effected or what is to be written in a bill of divorcement.
Image by Barbara Freedman, BarbaraFreedmanGallery.com.
Nevertheless, Jews sought to determine from the Torah all of the details of a complete legal system. As tradition describes it, from the time of the very giving of the written Torah, Moses already had received a companion Torah she'b'al peh (oral Torah), which he proceeded to teach to the people of Israel during their travels in the desert. It is clear that from the very beginning, Jews needed additional authoritative law, or halakhah ("going," or "path"), to govern regular life. These halakhot (plural) were passed on through the generations, and during the period of the Second Temple (fifth century BCE-first century C.E.), halakhot, both those developed through custom and those derived from interpretation of the Torah, were collected and transmitted. Following the destruction of the Temple in 70 C.E., the earliest rabbis gathered and transmitted the laws learned from earlier sages.
During the first two centuries, the rabbis apparently worked out how, as an educated leadership, they were to transmit and develop new law through agreed upon rules of interpretation. Much of our understanding of this period comes from later texts which were not intended as histories and which probably should not be relied upon for history. Nevertheless, it is clear that by the close of the second century, the rabbis had agreed on enough of the basics that their various opinions could be compiled and compared to each other. At this point, around the year 200 C.E., Rabbi Judah the Patriarch, used his unique position as a leader of the Jewish people who actually got along with the Romans to publish the first major Jewish work following the Bible, a study book of rabbinic law called the Mishnah (literally, teaching or repeating).