Sukkah, Chapter 3, Mishnah 5. Continuing the previous mishnayos, which deal with the disqualifications of the four species, the Mishnah now turns to the laws of the esrog.
"Esrog hagazul v'hayavesh - pasul" - a stolen esrog and a dried-out esrog are invalid:
"Hagazul" - a stolen esrog is invalid for two reasons: because of the requirement of "lachem," that the fruit must belong to him; and even in a case where technically it has become his, it is still invalid because of a mitzvah that comes through a transgression, since it came into his hands by way of a sin.
"Hayavesh" - a dried-out esrog is invalid because it is not beautiful, for it has lost its natural beauty.
"Shel asheirah v'shel ir hanidachas" - one that comes from an asheirah tree or from a condemned city:
An esrog that grew on a tree that was worshipped as idolatry, and likewise an esrog that comes from a city in which the majority of the inhabitants served idolatry, is invalid. The reason is that such objects must be burned, and since halachah requires that they be burned, we view them as though they had already been burned, so that they lack the required measure - the size needed to fulfill the mitzvah.
What is unique about the esrog: a fruit fit to be eaten:
The esrog differs from the other three species in that it is fit to be eaten, and because of this, additional laws apply to it:
"Shel orlah - pasul" - one that is orlah is invalid: the fruits of orlah are forbidden to derive benefit from, and it is impossible to gain any use from them. They therefore lack the requirement of "lachem," and the Mishnah likewise teaches that it is invalid because it is not fit to be eaten.
"Shel terumah temei'ah - pasul" - one that is impure Terumah is invalid: Terumah that became impure may not be eaten by anyone, and it is therefore invalid.
"Shel terumah tehorah - lo yitol, v'im natal - kasher" - one that is pure Terumah: he should not take it, but if he took it, it is valid:
Ideally one should not take an esrog of pure Terumah, but after the fact, if he did take it, he has fulfilled his obligation. The reason it is valid after the fact: even though Terumah may not be eaten by a Yisrael, it is permitted to a kohen, and that is enough for it to be considered "lachem." And the reason it may not be taken at the outset: since the esrog is held next to the lulav, and the lulav is kept in water, the esrog becomes susceptible to receiving tumah, and there is a concern that it will become impure through the touch of one's hands.
"Shel demai" - one that is demai: the dispute between Beis Shammai and Beis Hillel:
Demai is produce bought from an unlearned person, about which there is a doubt whether maaser was separated from it:
Beis Shammai invalidate it - since a person may not eat demai without first separating terumas maaser from it.
Beis Hillel validate it - since demai is permitted to be eaten by a poor person.
"V'shel maaser sheni biYerushalayim - lo yitol, v'im natal - kasher" - one of maaser sheni in Yerushalayim: he should not take it, but if he took it, it is valid:
Yerushalayim is the place where maaser sheni may be eaten, and nevertheless one should not take such an esrog at the outset, for the same reason given regarding pure Terumah: maaser sheni must be eaten in a state of purity, and there is a concern that through its contact with the wet lulav it will become susceptible to receiving tumah and will become impure. But after the fact, if he took it, it is valid.
In summary: In this Mishnah we learned the disqualifications of the esrog: a stolen one and a dried-out one (because of "lachem," a mitzvah that comes through a transgression, and the absence of beauty), one from an asheirah tree and from a condemned city (which must be burned and therefore lack the required measure), and one of orlah and of impure Terumah, which stem from what is unique about the esrog as a fruit fit to be eaten. We also learned the cases in which one should not take it at the outset but has fulfilled his obligation after the fact: pure Terumah and maaser sheni in Yerushalayim, as well as the dispute between Beis Shammai and Beis Hillel regarding demai.