What is the meaning of "Lechem Elokav"?
Rashi: It means the food of Hashem 1 with reference to the Korbanos.
Targum Onkelos and Targum Yonasan: It refers to the Korbanos.
Why does it say in Parshas Mumim 'say to Aharon', and it says in Parshas Temei'im (22:2) 'say to Aharon u'Vanav'?
Moshav Zekenim: Aharon was without any blemish, so the Parshah implies that he is told only regarding his descendants. Tum'ah could apply to him, so it was told to him and his sons together. Regarding a Metzora, it says (22:4) "mi'Zera Aharon", for this would not occur to Aharon himself - he was [like] an angel! It says Ish Ish to include Aharon, i.e. future Kohanim Gedolim. Alternatively, the Torah teaches him, for it does not rely on miracles, but it taught covertly, to hint that it would not occur to him. 1
Moshe had Tzara'as temporarily, Miryam for a week, and David for six months! One opinion in Shabbos 97a says that Aharon received Tzara'as [together with Miryam, just hjs departed right away]! Perhaps that opinion holds that the Torah taught covertly here, to avoid allusion to his Tzara'as. We find like this elsewhere (refer to 20:19:151:1).
What do we learn from "Ish mi'Zar'acha"?
Moshav Zekenim (from Chulin 24b): A minor is Pasul for Avodah. 1
Moshav Zekenim: The Kohanim did not allow one to serve until 20 years old. If he served, Tana'im argue about b'Di'eved, whether it is Pasul mid'Rabanan.
Why does it say "Asher Yihyeh Bo Mum"?
Moshav Zekenim (mostly from Sifra 3:2:2): This includes a Mum from before Matan Torah (unlike Zivah and Nega'im, which apply only to what arose after Matan Torah), and one born with a Mum, and a temporary Mum. 1
Moshav Zekenim: How can we learn all of these from one word? "Bo Mum" implies all of these. (Perhaps it learns from the repetition - it says "Bo Mum" also in verses 18 and 21! - PF)