A Jew who sells his field in Eretz Yisrael to a non-Jew is obligated every year to buy, even at great expense, the produce of that field in order to fulfill the mitzvah of bikkurim -- the bringing to the Beit Hamikdash and giving to the kohen a portion of the seven species for which Eretz Yisrael is praised. Although the mishna calls this a decree, the gemara explains that in essence one is obligated by Torah law to bring bikkurim from the field since the non-Jew's ownership does not exempt its produce from this obligation, as it is incumbent on the original owner.

Rashi elaborates on this point and distinguishes between the mitzvah of tithing and that of bikkurim. One is only obligated to tithe his agricultural produce if he is interested in eating or selling what remains after the tithing is done. Bikkurim, on the other hand, is a mitzvah which he must fulfill even if he has no benefit at all from the rest of the produce.

This distinction made by Rashi seems to run counter to the position taken by Turei Zahav (Shulchan Aruch Yoreh Deah 1:17) that one is obligated to tithe his produce even if he has no intention of eating from the remainder. Although he does not mention the above Rashi, Rabbi Akiva Eiger challenges the Turei Zahav's approach and cites the Magen Avraham (Shulchan Aruch Orach Chaim 8:1) as support for his opinion that both in regard to tithing baked products (challah) and raw grain there is no obligation to do so unless one wishes to eat from these foods.

Rabbi Zvi Hirsh Chayot points out that even though one is not obligated to tithe unless he intends to eat, on tithing he encounters two separate mitzvot. One is the tithing itself which removes the "tevel" status of the untithed produce and renders it permissible to eat. The other is the mitzvah of giving that tithe to the recipient designated by the Torah, such as teruma to the kohen. He cites early sources such as Ramban (Sefer Hamitzvot of Rambam, Shoresh 12) and the Tosefot Ryd (Kiddushin, Perek II) who point out the two mitzvot involved. This leads to the even more surprising revelation that although by Torah law even seperating one kernal for teruma is sufficient to remove the status of tevel from the produce, one does not properly fulfill the mitzvah of giving teruma to the kohen unless he separates a substantial amount to present to him in accordance with the Torah's instruction to "give him" his portion. Tosefot (Gittin 20a "dilma") seems to disagree with this distinction. (See also Responsa of Noda B'Yehuda Vol. II Yoreh Deah 201 who elaborates on this distinction.)

Guardians appointed by the court to manage the property of orphans must be extremely careful to do only what is in the best interest of their charges. They are therefore forbidden to sell fields in order to purchase slaves because they are swapping solid real estate for something of temporal value.

In the vicinity of Rabbi Meir there was a guardian who sold fields to purchase slaves and the sage stopped him from doing so. He subsequently heard a voice in a dream telling him "I intended for him to destroy and you directed him to build!"

"Dreams are meaningless" was Rabbi Meir's reaction and he persisted in preventing the guardian from destroying the estate he was in charge of.

Maharsha explains that the dream might otherwise have been interpreted as a heavenly message that it was the Divine Will that the property of the orphans should indeed be squandered because their father had acquired it in some illegal way such as theft, lying or usury.

Rabbi Meir's refusal to be influenced by dreams when acting according to the halacha is the point of this gemara, explains Iyun Yaakov. The same attitude of not swerving from what he considered right because of a dream is related in another incident concerning Rabbi Meir in Mesechta Horyot (13b). But it was not only dreams but any supernatural force which Rabbi Meir ignored when it came to doing his duty as a Jewish leader. This is evident from the incident which the gemara recounts immediately after the one about the dream.

There was a couple in Rabbi Meir's neighborhood who quarreled at the beginning of every Shabbat eve. The sage saw this as the work of Satan who wished to destroy their day of rest and he decided to intervene. He managed to restrain them from quarreling for three straight weeks and thus succeeded in restoring matrimonial harmony. The voice of Satan was then heard complaining: "Woe to the one whom Rabbi Meir has ejected from this home!"

Although Rabbi Meir sensed that this was no ordinary marital spat but the work of a destructive supernatural force, this did not deter him from fulfilling the mitzvah of creating peace between a man and his wife.