Explanation #1 (Rashi): He taught this here because he needs to teach "what is the source that we bathe a baby [on the third day from circumcision]?"

Objection #1: If so, [our Perek] should have begun with that Mishnah!

Objection #2: It should have taught it in Perek 19 (which discusses Bris Milah)!

Explanation #2: Rather, since the Tana taught above at the end of the previous Perek verses of Asmachta regarding Cheres, it teaches here also verses of Asmachta;

The verse "Tizrem..." is near the verse brought above "v'Lo Yimatzei vi'Mchitaso Cheres..."

Implied question: There is an opinion in Avodah Zarah (13a) that one may not benefit [from idolatry], but one may give benefit [to idolatry]!

Answer (Ri): That is only regarding [paying a] tax, which does not look so much that he intends [to benefit] idolatry. Rather, he gives it so they will let him pass. However, here it looks like he builds a house for idolatry.

Reference: In Avodah Zarah (47b), it asks that [through recessing into his own property], he allows more room for idolatry, and answers [that he uses the area for a privy, or fills the area with thorns].

Implied question: There is an opinion in Avodah Zarah (41b) that idolatry that broke by itself is permitted! (If so, why is it Tamei?)

Answer: The Yerushalmi establishes [that Mishnah] when he bowed to every stone, every piece of wood and every drop of earth. [Every fragment] is a total idolatry (by itself).

Question #1 (R. Tam): What is Rabanan's reason?

Suggestion: They hold like it says at the end of our Sugya (83b) that Tum'as idolatry is mid'Rabanan, and we make the Hekeshim to be lenient.

Rejection: If so, why does it have Tum'as Masa? We should say that the Hekesh to Nidah teaches that it does not apply to limbs, and the Hekesh to Sheretz teaches that it does not have Tum'as Masa!

Suggestion: Rabanan hold that we make the Hekeshim to be stringent.

Rejection: If so, we should say that the Hekesh to Nidah teaches Tum'ah Even Misma, and the Hekesh to Sheretz teaches that k'Adashah (the volume of a lentil) is Metamei!

Question #2: Also according to R. Akiva - if he makes the Hekeshim to be stringent, why does he need to say that the Hekesh to Sheretz teaches Meshamsheha (Kelim used for idol worship, that they have only Tum'as Maga)? He should say that it teaches that k'Adashah is Metamei!

And if he makes the Hekeshim to be lenient, it should not have even Tum'as Masa, and the Hekesh to Nidah [should teach] that it does not apply to limbs, and the Hekesh to Sheretz [should teach] that it does not have Tum'as Masa!

Question #3: We can ask similar according to R. Elazar, according to R. Akiva! (He says that the Hekesh to Nidah is stringent to teach Tum'as Masa, and the Hekesh to Sheretz is lenient to teach that Meshamsheha have only Tum'as Maga.)

Answer (R. Tam): The text in Seforim above says that Rabah said that "TiZRem" teaches one to consider idols foreign to himself, like a Zar. "Tzei Tomar Lo" (tell it to leave), but do not tell it to come;

Explanation: Since the Reisha [of the verse] already wrote "v'Timeisem Es Tzipuy Pesilei Kaspecha...", why does it need to say further "Tizrem Kemo Davah"? Rather, it teaches that one must distance greatly from it;

It comes to teach that even though the other verses are expounded leniently, because Tum'as idolatry is mid'Rabanan, we learn from Nidah to be stringent;

Therefore, Rabah says that all agree that it is Metamei b'Masa, for they expound "Tizrem". Also Rabanan would be Metamei through Even Misma like Nidah, if not that we exclude this due to the Hekesh to Sheretz.

Explanation #1 (Rashi): A rock is on pegs, and a Nidah sits on the rock. Kelim under the rock are Tamei from "v'Chol Asher Yihyeh Tachtav."

Question #1: In Toras Kohanim we learn Even Misma from "v'Chol ha'Mishkav", and the verse "Kol Asher Yihyeh Tachtav" we establish in Nidah (32b) to teach about Elyono Shel (something above a) Zav, and in Toras Kohanim we establish it for Merkav (a Kli made to ride on it)!

Question #2: If we learn from "Kol Asher Yihyeh Tachtav", if so, even Kelim that are not proper for Mishkav and Moshav [should be included], and in Toras Kohanim it is explicitly proven that Kelim that are not proper for Mishkav and Moshav do not have even light Tum'ah [through Even Misma]!

Question #3: Why does it mention a rock? [The same applies] even to a board on pegs!

Explanation #2 (R. Tam): Even Misma is a great rock that is heavy. The weight of the Zav or Nidah is not felt on the Kelim, due to the weight of the rock

"Misma" is a great load that requires putting, like it says "v'Heisayis Even Chada v'Sumas Al Pum Guba."

Question: In Toras Kohanim, it includes Even Misma from "v'Chol ha'Mishkav." This implies that we include it due to Mishkav u'Moshav;

In the entire Gemara, it connotes that we include it due to Masa, for in our Mishnah we call it Masa, and in Nidah (69b) a Mishnah teaches that a Zav and Zavah are Metamei b'Masa, and the Gemara explains that this refers to Even Misma!

Strengthening of question: In Nidah (55a), it excludes Dam Nidah from Tum'as Even Misma from "veha'Nosei Osam" is a Mi'ut [to exclude this].

Strengthening of question: In the Tosefta of Kelim (Bava Kama 6:1), it teaches that a Kli Cheres has Tum'ah only from its airspace and Heset of a Zav on Even Misma. Heset is Masa, like it says in Chulin (124b) "is carrying not Heset?!"

Inference: "On Even Misma" means that Kelim are on the rock. Mishkav u'Moshav does not apply at all!

[Also, we cannot say that Even Misma is due to Mishkav u'Moshav, for] Midras of a Kli Cheres is Tahor!

Answer: In Toras Kohanim it includes Even Misma due to Mishkav u'Moshav, i.e. when the Zav sits on it and the Kelim are underneath;

However, when the Tahor's hand or foot is under the Even Misma, it is due to Masa. The Tahor carries the Tamei;

Or, when the Zav's finger is under the rock, and the Kelim are on it, they are Tamei due to Heset of the Zav. This is "Masa of the Zav through Even Misma" of the Tosefta.

Question: In Nidah (54b) it excludes Dam Nidah from Mishkav u'Moshav from "Hi Yosheves." What was the question afterwards "just like she is Metamei through Even Misma, also Dam Nidah should be Metamei through Even Misma!"?

Since we already exclude Dam Nidah from Mishkav u'Moshav from "Hi Yosheves", what was the Havah Amina to say that it is Metamei through Even Misma?

Answer (Ri): From some Drashah we learn that [what became Tamei through] Even Misma is Metamei only food and drink. Therefore we need to exclude Dam Nidah even from Even Misma, which is a light Tum'ah. (I.e. not only it does not make Mishkav u'Moshav to be Metamei people. It is not even Metamei through Even Misma to be Metamei food and drink!)

Question: Why do we need Sheretz to exclude Even Misma? We already know this from the Hekesh to Mes (below, 83a)!

Answer: Since the verse revealed to us that you should estrange them from yourself like a stranger, we should equate [idolatry] to Nidah to be stringent. We would not learn from Mes to exclude idolatry from Even Misma, since we need the Hekesh to Mes for the Shi'ur of a k'Zayis.

Alternatively, [we need the Hekesh to Mes to teach] like it says in Sanhedrin (47b) that just like attached idolatry does not become forbidden, also an attached grave is not forbidden.

Question (Ri): What was the question? We need to exclude that it is not Metamei in Ohel ha'Mes!

Perhaps we do not learn from any leniency from Nidah, for Rav Chama bar Gurya below asked whether or not it applies to limbs, even though Nidah does not apply to limbs!

Answer: We properly learn from Nidah that idolatry does not have the stringency of Mes. Even though the Hekesh to Nidah is to be stringent, we can learn also a leniency from it.

Implied question: [If we can learn also leniencies from Nidah,] why [was Rav Chama bar Gurya] unsure whether or not it applies to limbs?

Answer #1: This is because it is different. A person cannot reassemble limbs of a Nidah, but a craftsman can reassemble limbs of idolatry.

Answer #2: This that it says "for what Halachah was it taught?", and the answer "for Meshamshin", was if you will say that we learn a leniency from Nidah.

Explanation (Rashi): [R. Akiva holds that] Kelim that serve idolatry do not have Tum'ah through Masa or Even Misma.

Inference: If not for the Hekesh to Sheretz, they would be Metamei like idolatry through Even Misma.

Question: According to Rabanan, the Hekesh to Sheretz does not come for Meshamsheha. What is the source that Meshamshin do not have Tum'as Masa like idolatry itself?

Below, Rav Ashi says according to Rabah that Meshamshin, whether they moved others or others moved them, are Tehorim (unlike idolatry itself)!

Answer (Ri): If not that Meshamshin are equated to a Sheretz, [Rabanan] would not be Metamei them at all. (I.e. the verse equates Meshamshin themselves to a Sheretz, like Tosfos proceeds to explain);

Rabanan are Metamei Meshamshin because it says "Shaketz Teshaktzenu... Ki Cherem Hu." This implies that anything that is Cherem, i.e. Asur b'Hana'ah, is [Metamei] like a Sheretz, and Meshamshin are Asur b'Hana'ah.

Implied suggestion: Perhaps we could answer for Rashi (that Rabanan expound similarly to R. Akiva, that the Hekesh to Sheretz excludes Meshamshin from Tum'as Masa)!

Rejection: "Ki Cherem Hu" does not connote to exclude Meshamshin, that they do not have Tum'as Masa. There is nothing extra for this. (I.e. if the Havah Amina was that Meshamshin are Tamei like idolatry itself, nothing is extra to teach that they are not. Rabanan need Ki Cherem Hu to exclude idolatry from Even Misma. However, R. Akiva needs Ki Cherem Hu only to teach that Meshamshin are unlike idolatry itself.)

However, this that Meshamshin are Tamei, it properly connotes.

Observation: Regarding the Hekesh [of idolatry] to a Mes (83b), we cannot ask that [rather,] it should be equated to a Neveilah, for we need [the Hekesh] to a Mes like we expound in Sanhedrin (47b. Just like idolatry attached to the ground is permitted, attached dirt of a grave is permitted.)

Explanation (Rashi): We ask that we should equate [idolatry] to a Neveilah, for then we would not need to make a Hekesh to a Sheretz.

Explanation #1 (Rashbam): In R. Elazar's words, the text does not say "according to R. Akiva, for what Halachah was [idolatry] equated to a Sheretz? It was for Meshamsheha", for we need [the Hekesh] to exclude from Even Misma;

This is like it says, that all agree that it is not Metamei through Even Misma, for it is equated to a Sheretz.

Explanation #2: Some texts do not say "for it is equated to a Sheretz." According to this, we can say that R. Elazar's reason that all agree that it is not Metamei through Even Misma is not due to a Hekesh to a Sheretz. Rather, without anything extra, we are not so stringent to be Metamei through Even Misma.

Consequence: According to this, the text properly says "according to R. Akiva, for what Halachah [was idolatry equated to a Sheretz]?"

Explanation #2 (cont.): Afterwards, it asks "the Torah should equate [idolatry] to a Neveilah!" We do not ask that it should equate it to a Neveilah, and then it need not equate it to a Sheretz, for also now it need not equate it to a Sheretz for this (to exclude Even Misma);

Rather, it asks that it would be better to equate it to a Neveilah, for it truly resembles a Neveilah, but it does not resemble Nidah, for Nidah is Metamei through Even Misma, but idolatry is not.