QUESTION: The Gemara says that since Aharon ha'Kohen was not counted among the Leviyim during their census, the rule that "a Levi and his animals exempt Kedushah of Bechor from others" does not apply to him. The Gemara asks that since Aharon and his animals did not exempt others from Bechorah, he and his animals should not be exempt themselves.
From what type of Bechorah is the Gemara asking that Aharon should be exempt?
(a) TOSFOS (DH v'Aharon) explains that Aharon himself was not a Bechor. Miriam was born three years before Aharon (Shemos Rabah 1:13; see also RASHI to Shabbos 86a, DH Al Yedei Telisa'i). Tosfos says that it is obvious that the Gemara is asking only that Aharon's animals (firstborn donkeys) should retain their Kedushah.
(b) Tosfos quotes the words of RASHI (which do not appear in our text of Rashi) who asserts that Aharon himself should have retained the Kedushah of a Bechor, implying that he indeed was a Bechor. This is supported by a different Midrash (Bamidbar Rabah 6:2) that says that "Kehunah was given to Aharon because he was a Bechor." This opinion is also expressed by the MAHARSHA in Sanhedrin (7a; see Insights to Sanhedrin 7:1; see also RASHBAM to Bereishis 28:9 and Shemos 15:20).


QUESTION: Rebbi Chanina says that one sheep of a Levi exempted many firstborn donkeys of a Yisrael.
Why does Rebbi Chanina not mention also that one sheep of a Levi exempted many firstborn Kosher animals of a Yisrael? The Gemara earlier (4a) says that they exempted even the Yisrael's firstborn Kosher animals!
(a) TOSFOS (4a, DH v'Od) explains that Rebbi Chanina is discussing only the type of animal that can be redeemed in some form today (because he is comparing the way a Peter Chamor was redeemed in the times of the Midbar to the way it is redeemed now). Since there is no redemption for a Kosher animal today, he does not discuss the redemption of the Kosher animals in the Midbar.
(b) Tosfos answers further that Rebbi Chanina mentions the ability of one sheep of a Levi to exempt multiple animals of a Yisrael only because it has ramifications for Pidyon Peter Chamor today. The Halachah of the Levi's sheep in the Midbar teaches that a single sheep may be re-used for Pidyon Peter Chamor multiple times. A Kosher animal, in contrast, can never exempt another Kosher animal, and thus Rebbi Chanina has no need to mention the fact that one animal of a Levi was able to exempt numerous Kosher animals of a Yisrael when the Jews were in the Midbar.
(c) The SEFAS EMES points out that RASHI (to Bamidbar 3:45) writes that the Levi's firstborn Kosher animal did not exempt the Yisrael's firstborn Kosher animal in the Midbar. (The MIZRACHI suggests that perhaps Rashi understands that Abaye (on 4a) disagrees with Rava and maintains that the firstborn Kosher animal of the Yisrael was not exempted from its Bechorah. Thus, Rashi on the verse is stating Abaye's opinion.)
QUESTIONS: The Gemara records a dispute between Reish Lakish and Rebbi Yochanan regarding the firstborn male children and animals that were born when the Jewish people were in the Midbar. Rebbi Yochanan maintains that those firstborn people and animals were Kadosh with the Kedushah of Bechor. Reish Lakish maintains that they were not Kadosh with the Kedushah of Bechor.
The Gemara later quotes some who say that Reish Lakish challenged Rebbi Yochanan's view from a Beraisa. The Beraisa states that on the day on which the Mishkan was erected in the Midbar, "Bechoros" were offered as Korbanos on the Mizbe'ach. Reish Lakish asserts that this implies that only on that day were Bechoros offered, but not afterwards. (RASHI (DH u'Minah) points out that on that day, all of the firstborn animals that came out of Mitzrayim were offered as Korbanos.)
Rebbi Yochanan rejects this proof and asserts that, on the contrary, from that day onward Bechoros were brought to the Mishkan, not only on the day on which the Mishkan was erected. The Chidush is that before the Mishkan was erected, Bechoros were not brought at all. The reason for this is that obligatory Korbanos ("Chovos") may not be offered on a Bamah, a private altar. Before the Mishkan was erected, individuals were not permitted to build altars on which to offer Bechoros or any other obligatory Korbanos may not be offered on a private Bamah.
The rule that obligatory Korbanos may not be offered on a private Bamah seems to be contradicted by the account in the Torah (Vayikra 8) of the seven days of Milu'im. On each of the seven days before the Mishkan was erected (see Rashi to Vayikra 9:1), a Korban Chatas was offered (see Vayikra 8:14 and 8:33-35). A Chatas, however, is a Korban Chovah, and nevertheless it was offered on a private Bamah before the Mishkan was erected!
There is a similar question on the words of TOSFOS in Avodah Zarah (34a). The Gemara in Ta'anis (11b) asks about what garments Moshe Rabeinu wore during those seven days of Milu'im. Tosfos in Avodah Zarah (34a, DH ba'Meh) asks why it is not obvious that Moshe Rabeinu wore the Bigdei Kehunah. Tosfos answers that since, throughout the seven days of Milu'im, Moshe Rabeinu set up the Mishkan and afterwards dismantled it (see Rashi to Vayikra 9:23), it still had the status of a private Bamah, and one may not wear Bigdei Kehunah when he offers a Korban on a private Bamah. (The Gemara in Ta'anis concludes that Moshe Rabeinu wore a white robe during the Milu'im.)
If the Mishkan had the status of a private Bamah during the seven days of Milu'im, as Tosfos writes, then how were they permitted to offer a Korban Chatas on it?
ANSWER: The SHITAH MEKUBETZES (#3) answers that when the Gemara says that before the Mishkan was set up the offering of obligatory Korbanos on a Bamah was prohibited, the Gemara refers to the private, individual Bamah that each person was permitted to build in order to offer voluntary Korbanos. In contrast, the Mishkan, during the seven days of Milu'im, before it was erected permanently, had the status of a public Bamah (Bamas Tzibur). Therefore, the Korban Chatas could be offered there.
The reason why Moshe Rabeinu could not wear the Bigdei Kehunah when he offered the Korbanos in the Mishkan during the seven days of Milu'im was that the Bigdei Kehunah had not yet been worn by Aharon and had not yet been anointed for use. (D. BLOOM)