The Mishna (2a) taught that the laws of yedi’ot ha-tumah – situations where a person forgot that he was ritually defiled and entered the Temple or ate consecrated food – are “two that are four.” That is to say that there are different situations regarding how the mistake was made – as noted he could have forgotten his status and either entered the Temple or eaten consecrated food – or he could remember his status but forget that the food was consecrated or that it was forbidden for him to enter the Temple in this state. These are the situations referred to by the Torah when it says (Vayikra 5:2-14) that the sinner must bring a korban oleh ve-yored – a “sliding scale” sacrifice where a wealthy person will bring goat or a lamb, a middle income person will bring a dove and a poor person will bring a meal offering.
The Gemara on today’s daf asks how we know that these laws apply specifically to the Temple and to food consecrated to the Temple, since the Torah itself simply says that the person erred, was ritually impure and was guilty, without specifying what he was guilty of. In response, Rabbi Yehuda HaNasi suggested a gezera shava – a method of comparing similar words that appear in two places in the Torah. Rabbi’s statement was praised by Rava, who said that Rabbi “drew up water from deep wells” in suggesting this.
Rava’s praise is questioned by a number of the commentators, who point out that the rule of a gezera shava is that it must be received as a tradition; no Rabbi, however great he may be, can create one on his own. It is therefore difficult to understand why it is so impressive from Rabbi to simply repeat a teaching that he had received from others. The Ritva and others suggest that Rabbi’s tradition was limited to the knowledge that this particular word had a gezera shava attached to it. His greatness was to work out the significance of that teaching.