What does "Chayos" and "Tehoros" come to teach?
Rashi: "Chayos" comes to preclude T'reifos; "Tehoros" excludes Tamei Asherspecies of birds. 1
Ramban #1 (citing Toras Kohanim): "Chayos" comes to preclude slaughtered birds, and "Tehoros" excludes both Tamei Asherspecies and T'reifos (which are Tamei, i.e. forbidden, to you).
Moshav Zekenim, citing R. Eliezer of Garmaiza: "Chayos" implies zealous, like "Ki Chayos Henah" (Shemos 1:19). It need not teach that they are alive, for he slaughters one!
See Ramban's objections to this explanation. Asher
He writes this after citing the Ibn Ezra, who, (based on Pesukim in Tehilim and in No'ach and Lech-L'cha), explains that it incorporates all types of birds, and after concluding (based on Pesukim in Shoftim, Ki Seitzei and elsewhere) that it pertains to small birds that sing in the morning ('Tzafra' is the Arama'ic word for morning).
What is the significance of (a) the birds, (b) the cedar-stick (c) the crimson thread and the hyssop ("Sh'ni Tola'as")?
Rashi and Ramban: (a) Because the primary sin for which Tzara'as comes to atone is Lashon ha'Ra (baseless twittering), the Kaparah; requires birds that twitter; 1 (b) Since the root of Lashon ha'Ra is pride, he must take a stick from a tall cedar 2 (c) and he must make himself small like a crimson thread 3 and a hyssop. 4
Rosh: He brings birds due to "k'Tzipor Nodedes Min Kinah Ken Ish Noded mi'Mkomo." This is like a Metzora, who dwelled outside the Machaneh.
Moshav Zekenim, citing Ibn Ezra: We find crimson thread and hyssop also for Taharah of Bayis ha'Menuga and from Tum'as Mes; they are like Pesach Mitzrayim (in which they put blood on the doorpost via hyssop - Shemos 12:22).
Moshav Zekenim: If his heart was high and haughty like cedar, and his Aveirah is crimson ('Im Yihyu Chata'eichem ka'Shanim" (Yeshayah 1:18), and his Yetzer Tov is lowly like hyssop, all will be atoned for in the merit of killing his Yetzer ha'Ra.
Moshav Zekenim (57, also in Otzar Midrashim Pinchas ben Ya'ir with changes): Tzara'as comes for three matters - for envy of folly, like Miryam 5 ; for lust of wealth, like Gechazi; and for haughtiness, like Uziyah. Therefore, his clothes are torn and his hair grows long, against wealth; he calls 'Tamei, Tamei', against desire for folly; he dwells alone because he raised himself; he dwells outside all three camps. Therefore, he brings three [matters for] Kaparah - cedar, crimson thread and hyssop.
Moshav Zekenim: All slander is said quietly and covertly, and the words are changed so [the one slandered] will not understand if he hears. Therefore, his Kaparah and cure is through birds that twitter and do not have nice speech. Also refer to 14:4:1:3***.
Which is the tallest tree (Ramban).
Or like a worm (which also translates as 'Tola'as').
Which is the smallest of plants (Ramban).
This is difficult. Miryam spoke, for she thought that Moshe improperly divorced his wife! Perhaps 'Kin'as ha'Hevel' means a zealousness of folly (it was proper to question Moshe's act, but it was folly to speak to Aharon, and not Moshe himself). Or, it is a desire for folly, i.e. to speak unnecessary words; Mashehu of this was mixed with her pure intent (to help Tziporah), and Hashem is ultra-exacting with great Tzadikim. (PF)
QUESTIONS ON RASHI
Rashi writes that "Chayos" comes to exclude T'reifos. We need it to exclude birds missing a limb!
Moshav Zekenim citing Ri: 'Chayos' excludes both of these. 1
Moshav Zekenim: Regarding Noach, we need two verses - "mi'Kol ha'Chai" to teach that their extremal limbs are alive, and "Lehachayos Itach" to exclude Tereifos (Zevachim 116a)! There, to repopulate the world, we would have thought that there is concern only that they are not Tereifos, if not for a second verse.