Why Are There 39 Types of Work Forbidden on Shabbat
People familiar with the Sabbath laws know that the Torah does not list the activities prohibited on the Sabbath. However, rabbis in the Babylonian Talmud, Shabbat 49a, state that the Torah hints at the activities that are banned.
These hints are based on two rabbinical teachings that are applied by the rabbis at times: (1) When facts or incidents are placed near one another in the Bible, one can derive a lesson from the juxtaposition. (2) A halakhah can be learned from such things as counting the number of times an item appears in the Torah.
Thus the rabbis stated: