צַו אֶת אַהֲרֹן וְאֶת בָּנָיו לֵאמֹר זֹאת תּוֹרַת הָעֹלָה
Command Aaron and his sons saying, this is the law of the burnt-offering (Leviticus 6:2)
See the Ramban who wrote that it was not in reference to this verse that R. Simon made his comment, because under the law of the burnt-offering (עֹלָה), the priest suffers no economic loss in bringing the offering to the altar. On the contrary, the priest enjoys an economic gain from bringing a burnt-offering to the altar, because the animal's hide becomes the possession of the priest.
However, our master says that the words of R. Simon were indeed based on this verse and were built on a foundation of reason. For it is written in the Midrash Rabbah (Leviticus 7:1) commenting on this verse.
This is explained by the verse (Proverbs 10:12): "Hatred stirs up quarrels" (שִׂנְאָה תְּעֹרֵר מְדָנִים). The Midrash goes on to explain at length that the hatred that Aaron aroused (see Deuteronomy 9:21) by making the Golden Calf provoked many adverse judgments, and Aaron's name was therefore not mentioned from the beginning of the book of Leviticus until this verse, except for verses such as (Leviticus 1:8) "and Aaron's sons, the priests, will lay the pieces" (וְעָרְכוּ בְּנֵי אַהֲרֹן הַכֹּהֲנִים אֵת הַנְּתָחִים). Only the prayer of Moses succeeded in drawing Aaron close to the Eternal again. It was, therefore, appropriate that the first commandment given to Aaron after he was brought close should contain an admonition about the sin that he committed.
Our master has already explained at length that the sin of the calf occurred because the Israelites refused to listen to the voice of the living G-d and because, despising the study of the Torah, they preferred performing commandments at the instruction of mortals to learning the commandments through the study of Torah. And Aaron, too, had held that opinion. Thus, after Moses prayed to the Eternal in behalf of Aaron, and G-d drew Aaron close to perform the priestly service before Him, G-d taught Aaron that although He henceforward would desire burnt-offerings and sacrifices, and those sacrifices would ascend in favor before Him, nevertheless the lips of the priest should guard wisdom (שִׂפְתֵי כֹהֵן יִשְׁמְרוּדַעַת). It would be Aaron's responsibility to teach the people that obeying is better than any sacrifice and acts of justice and charity are preferred by the Eternal to oxen and bullocks. The people would then learn to seek the Torah from his mouth and consequently would not bring numerous sacrifices in order to eat meat, for study, which leads one to perform good deeds, is greater than anything.
This is what was told to Aaron. "This is the law of the burnt-offering" (זֹאת תּוֹרַת הָעֹלָה), "it is that [i.e., the law of the burnt-offering] which goes up" (הִוא הָעֹלָה). For the essence of the burnt-offering is the law of the burnt-offering. As our Sages say, whoever studies the law of the burnt-offering, is considered by the Scripture to have offered the burnt-offering. And, as we have written at length in poroshat Vayiqra, the law of the burnt-offering is more sublime than the burnt-offering itself.
This admonition therefore required an added exhortation, because it implied an economic loss to the Priests. For if they teach the people to understand what the Eternal is asking of them, then the people, once having understood that the true essence of the burnt-offering is the law of the burnt-offering, would stop offering sacrifices. But if they do so, then the Priests will forego the breast of waving (חֲזֵה הַתְּנוּפָה) and the thigh of heaving (שׁוֹק הַתְּרוּמָה).
וְחֵלֶב נְבֵלָה וְחֵלֶב טְרֵפָה יֵעָשֶׂה לְכָל מְלָאכָה וְאָכֹל לֹא תֹאכְלֻהוּ
And the fat of the beast that dies of itself, and the fat of that which is torn by beasts, may be used in any other use; but on no account shall you eat it. (Leviticus 7:24)
In the Talmud, it is asked why it is written here "on no account shall you eat it" (וְאָכֹל לֹא תֹאכְלֻהוּ). For is it not prohibited to eat even the fat (וְחֵלֶב) of a properly slaughtered animal, so why was it necessary to mention that the fat of a beast that dies of itself (נבלה) or that which is torn by beasts (טרפה) may not be eaten? And in the Talmud they deduced what they deduced. There is, moreover, a further question. Why is it written "may be used in any other use (יֵעָשֶׂה לְכָל מְלָאכָה)? It should have said "a service may be performed on it" (יֵעָשֶׂה בּוֹ מְלָאכָה).
And it appears to our master that although the Torah made it permissible for work to be performed with heilev or for heilev to be sold, if the hands of a person are constantly coming into contact with heilev, there are grounds for suspecting that he may come to eat it. Therefore, anyone that wishes to be involved in work that brings him into constant contact with heilev, must first make it unfit for human consumption so that there is no risk that he might eat it. Thus, in Pesahim 20 it is written that they stored heilev in a disgusting container. Thus, the verse "the fat of a the beast that dies of itself and the fat of that which is torn by beasts may be used in any other use" means that one should render such fat unfit to be eaten and fit only for the work to be performed on it, so that "on no account shall you eat it."