Sukkah 027

1:
We have already explained why one cannot perform the mitzvah with any one of the four species (or all four of them!) that does not lawfully belong to the user. Let me remind you of what I wrote in Sukkah 025:

This requirement derives from a careful examination of the Hebrew text of the Torah [Leviticus 23:40]:

The almost enclitic "for yourselves" was understood by the sages as implying that the lulav must belong to the person using it. This means that a stolen lulav is invalid, not only for ethico-halakhic reasons but also for liturgic-halakhic reasons.

2:
We have, in fact, also explained why an etrog which has dried up is invalid as one of the four species. Again in Sukkah 025 I wrote:

The Hebrew phrase literally translates "fruit of a glorious tree". The sages held that the adjective 'glorious', 'stately', 'majestic' should be applied to all four items and not just to the etrog.

Obviously, a withered etrog does not express hopes for abundant rain, which is so desired in the climate of Eretz-Israel.

3:
We have also explained the terms asherah and 'apostate town'. See, yet again, Sukkah 025.

4:
We must now explain the term orlah (in the context of the etrog). The Torah [Leviticus 19:23-25] forbids us to eat the fruit of a newly planted tree during the first four years of its life. Only in the fifth year may the fruit be eaten:

Fruit from a newly-planted tree during the first three years of its life is called orlah. This includes, of course, an etrog. The Torah explains that the fruit of the fourth year is not to be eaten but to serve as a thanksgiving offering.

5:
During the years of our study we have explained the term terumah many times. It refers to foodstuffs — usually wheat — which have been given by an agriculturist to the kohen [priest] of his choice as required by Torah law. Terumah which has become ritually impure may not be eaten. This is why a priest who received an etrog as terumah and which subsequently contracted ritual impurity may not use it in order to fulfill the mitzvah of the four species.

6:
It would seem logical that a kohen should be able to use for the mitzvah of the four species an etrog which he received as terumah and which is still in a state of ritual purity. Nevertheless, our mishnah indicates that ideally such an etrog should not be used. When we studied Tractate Yadayyim we learned about the various ways in which foodstuffs which are ritually pure can contract ritual impurity, one of which is contact with moisture. When the priest brings the etrog into contact with the other three species, which are usually damp, he thereby makes it possible for the etrog to become ritually impure (because it has already been dampened). Since terumah is sacred it should not be treated so cavalierly.

7:
However, if the etrog which was terumah was used for the mitzvah the ritual has been properly performed; it's just that it would have been better to use an etrog which was not terumah.

8:
Demai is a technical term which describes produce whose status regarding tithes cannot be ascertained. Many times we have explained that certain deductions had to be taken from produce from field and orchard: some were to be given to a Levite (who also had to give some of his tithe to a priest), and some was to be given to the indigent. Ordinary people who tried to be observant Jews refrained from eating such produce. Therefore, ideally, an etrog which is demai should not be used, and this is the final word of the School of Shammai. However, if it were, nevertheless, used the mitzvah has been properly fulfilled because demai could be eaten by indigent people; this is the conclusion of Bet Hillel (whose view is accepted halakhah).

9:
In some years of the seven-year agricultural cycle which ends with shemittah year the tithe was not given to the indigent but taken to Jerusalem to be eaten there. The same rule applies to this tithe: ideally it should not be used but if it were used the mitzvah has been properly performed.