1) THE SHIRT ON HIS BACK
OPINIONS: The Beraisa states that the Tzadikim who lived in an Ir ha'Nidachas and who did not join the other residents in serving Avodah Zarah are permitted to leave. Their possessions, however, are gathered with the possessions of the other residents of the city and burned. Rebbi Shimon explains that the reason why their possessions are burned is that it was their possessions -- their desire for financial gain -- that led them to live in the city of evildoers, and therefore they are punished by having their possessions destroyed.
When the people who did not serve Avodah Zarah depart and leave behind their belongings, are they permitted to take some clothes with them, or must they leave all of their clothes and depart the city completely unclad, without even a shirt on their backs?
(a) RASHI in Erchin (7b, DH Se'ar Nashim Tzadkaniyos) quotes the Gemara here in Sanhedrin and writes that the Tzadikim who lived in an Ir ha'Nidachas must leave the city "Arumim," unclad, implying that they must leave without any of their clothes.
The ARUCH LA'NER points out, however, that Rashi here says that the clothes on their backs are not burned. The phrase "Arumim" in Rashi in Erchin, therefore, does not seem to be intended in its literal sense.
The BEIS YITZCHAK (OC 14) argues that if, according to Rashi's Girsa, the expression used is "Arumim," then it is to be understood literally, because otherwise the Gemara would have said that they go out of the city "devoid of their possessions." The choice of this phrase indicates that they leave entirely unclothed.
The CHIDA (in BA'ALEI BRIS AVRAHAM) proves that "Arumim" does not necessarily mean naked. The verse in Yeshayah (20:3) says that the servant of Yeshayah went "Arum v'Yachaf" -- "naked and barefoot" for three years. Rashi there explains that this means that he went with torn and worn clothes, but not that he wore no clothes at all. This is evident from the fact that the verse mentions that the servants there were wearing a "Sak" (sackcloth).
(b) The MINCHAS CHINUCH writes that the answer to this question depends on the argument between Rebbi Shimon and the Tana Kama. Rebbi Shimon expounds the reasoning of Mitzvos in order to determine the proper Halachah. Accordingly, even though their possessions caused them to live among evil neighbors, since they would be clothed wherever they would live, the clothes on their bodies are not included among the possessions which must be burned. According to the Tana Kama, the verse states that all of their possessions must be burned. This includes everything, including whatever clothes they might be wearing. (Y. MONTROSE)
2) "MA'ASER SHENI" WITHIN THE WALLS OF YERUSHALAYIM
OPINIONS: The Gemara cites a Beraisa in which Rebbi Meir and the Chachamim disagree with regard to the obligation to separate Chalah from dough of Ma'aser Sheni. Rebbi Meir maintains that the dough is exempt, while the Chachamim maintain that it is obligated. Rav Chisda explains that their argument applies only to dough of Ma'aser Sheni that is within the walls of Yerushalayim. Rebbi Meir maintains that it no longer belongs to the owner, but to "Gavoha," while the Chachamim maintain that it still belongs to the owner. Everyone agrees that dough outside of Yerushalayim is exempt from Chalah; since the owner is prohibited to eat the bread of Ma'aser Sheni outside of Yerushalayim, the obligation of Chalah does not take effect (see Rashi).
Rav Yosef challenges Rav Chisda's explanation (that everyone agrees that dough of Ma'aser Sheni outside of Yerushalayim is exempt from Chalah) from the Tosefta cited earlier in the Gemara. The Tosefta discusses the procedure for the proper disposal of various types of consecrated items that were in the possession of the people of an Ir ha'Nidachas. The Tosefta states that fruits of Ma'aser Sheni should be hidden away (in "Genizah"). Where is this Ma'aser Sheni located? The Tosefta cannot be referring to Ma'aser Sheni that was in Yerushalayim, because Yerushalayim cannot become an Ir ha'Nidachas, as a Beraisa teaches. If the Ma'aser Sheni was brought to Yerushalayim to be eaten at the time that its city of origin was found to be an Ir ha'Nidachas, then the walls of Yerushalayim "save" it from being burned with the possessions of the Ir ha'Nidachas. It must be that the Ma'aser Sheni is outside of Yerushalayim, in its city of origin, and yet the Tosefta says that it must be hidden away. According to Rav Chisda, everyone agrees that Ma'aser Sheni belongs to "Gavoha" when it is outside of Yerushalayim, and thus it should be permitted to be eaten (in Yerushalayim) and it should not need to be hidden away!
The Gemara concludes, according to Rav Chisda, that the Tosefta is referring to Ma'aser Sheni that was brought to Yerushalayim when the walls of Yerushalayim were no longer standing. Consequently, the walls are unable to "save" the Ma'aser Sheni from being considered the property of the Ir ha'Nidachas, and thus the Ma'aser Sheni must be hidden away.
What exactly is the power of the walls of Yerushalayim to "save" Ma'aser Sheni?
(a) The RAN explains that the ability of Yerushalayim to remove the prohibition that applies to possessions of an Ir ha'Nidachas is based on the law of a "Pikadon" in an Ir ha'Nidachas. If a resident of a city deposits an item for safekeeping with a trustee outside of the city, and then the city becomes an Ir ha'Nidachas, the deposited item does not need to be burned with the rest of the possessions of the Ir ha'Nidachas. This law is derived from the verse that commands to "gather together all of its possessions to the middle of its main street..." (Devarim 13:17). Since a possession that is in a different city cannot be gathered together with the rest of the possessions in the Ir ha'Nidachas, it is not included in the Torah's decree. Ma'aser Sheni in Yerushalayim is considered like a Pikadon that was deposited in a different city. Moreover, it is even less possible to gather it together with the rest of the possessions of the Ir ha'Nidachas, since Ma'aser Sheni may not be removed from Yerushalayim once it is brought there. Therefore, when the Gemara says that the walls "save" the Ma'aser Sheni, it means that the Ma'aser Sheni's permanent place is in Yerushalayim and it cannot be gathered together with the rest of the possessions of the Ir ha'Nidachas. (The Gemara concludes that only when the walls are standing is the Ma'aser Sheni considered to be in a different city, but not when there is no wall.)
(b) The RA'AVAD explains that the words "and the case is when the walls [of Yerushalayim] fell" are not the correct text in the conclusion of the Gemara and should be omitted. He explains that even when the walls are standing, the concept that the walls can "save" Ma'aser Sheni is only mid'Rabanan, according to Rava. Consequently, the walls cannot affect a Torah law, such as the requirement to burn (or properly dispose of) all of the possessions of an Ir ha'Nidachas. Therefore, the Ma'aser Sheni must be hidden.
The Ran rejects this logic. He asserts that even if the concept of "Mechitzos Koltos" is only rabbinical, the Torah does not declare that the status of every item must remain the same forever. If the Rabanan declare that a certain item is declared as part of a city (such as Ma'aser Sheni within the walls of Yerushalayim), then the Torah does not include that in what must be "gathered together" in another city (in the Ir ha'Nidachas).