Rashi was bothered by the verse’s seemingly unnecessary continuation: Once the verse states, “Their flesh shall be yours,” why does it need to continue to say, “like the breast of the waving and the right thigh”? Therefore, this additional phrase must be teaching us some new law. And it does not stand to reason that it merely means to equate the firstborn animal to the peace offering in respect to the time-limit of its consumption. For if that were the case, then the verse would not need to allude to the law, it could just say so explicitly. Rather, the verse must have intended to teach two laws, and used the comparison to the peace offering for brevity’s sake.
Therefore, both laws of the peace offering apply to the firstborn — who partakes in its consumption, and how long it is eaten for. Rashi did not actually leave out the first law, we are just reading it incorrectly. We have to see both of Rashi’s comments as being one continuous comment, as follows:
Like the breast of the waving and the right thigh — Of the peace-offering which is eaten by the kohanim, their wives, their children and their slaves for two days and one night. So, too, the firstborn animal.
Rashi does not spell out the two laws learnt from the peace offering, he simply says that both of these apply to the firstborn. Then he refers back to the law of how long it is eaten for: “It is eaten for two days and one night.” This law, Rashi is saying, requires further clarification, and it is for this purpose that he cites Rabbi Akiva:
“It shall be yours,” Rabbi Akiva came and taught: [By repeating the words “shall be yours”] Scripture adds another ‘being,’ so that you should not say [that it is] like the breast and thigh of the thanksgiving offering, which is eaten only for [one] day and [one] night.”
The comparison to the “breast and thigh” is not enough here, for it can be referring to the thanksgiving offering which has a shorter time span. Therefore we require Rabbi Akiva to “come and say,” to conclusively prove that it is the peace offering meant here, and that is by the verse’s reiteration, “it shall be yours.”
Rabbi Akiva is specifically mentioned because his general understanding is that “Torah does not speak in the language of man,” and therefore, when there is a repetition in the Torah, we do not say that the Torah is simply mirroring human speech, but rather, that it is intentionally alluding to a new law or detail.
