Yevamot 30 - 36
Rava said, “I consider it as if he had done two transgressions, but he is only obligated for one.”
This enigmatic statement refers to a case where a man transgressed with his brother’s wife, who after his marrying her sister was also his wife’s sister as well, and might be prohibited for these two separate reasons. Rava explains in our gemara, however, that Rabbi Yosi in our sugya holds that “something prohibited cannot gain an additional prohibition; something cannot be more prohibited than prohibited!
Therefore, Rava teaches that Rabbi Yosi really meant that in some sense the person who transgresses in this way is viewed “as if he transgressed two prohibitions” — but he does not actually need to bring atonement for the two separate prohibitions. For example, he would not bring two chatat offerings to the Beit Hamikdash if he transgressed in a shogeg manner (unintentional yet negligent) and the transgression was punishable by karet expiation.
So what is the significance of saying “It is as if he had done two transgressions” asks the gemara? “To bury him in the place where completely wicked people are buried” answers the gemara — even after death in this world he is buried in a separate place in the cemetery reserved for the worst offenders, such as those given the capital punishments of sereifa (“burning”) and sekila (stoning”) (Rashi).
- Yevamot 32b
The Sage Abaye said, "The Sages were stricter at times in regard to the Rabbinical laws they enacted than they were in regard to Torah laws."
The Torah laws given at Sinai are understood to have a “stronger” and “more severe” standing than the later Rabbinical laws enacted to serve as a safeguard for fulfilling the Torah’s teachings. However, when the Sages felt that people might not be careful in accepting and keeping their laws as seriously as necessary, special penalties were imposed by the Sages that are not found in similar Torah laws, which by their nature were taken more strictly and not likely to be transgressed even without any additional penalty (Rashi).
- Yevamot 36b