Arachin 3b — ערכין ג:

It includes slaves. Rashi explains that a man has a Canaanite slave whom he wants to sell. If the slave wants to be sold only in Eretz Yisrael, the master is made to take him there. Tosafot note that Rashi explains it differently in Ketubot.

And according to the version of the Mishnah that names slaves outright, whom does "everyone" include?

A move from a pleasant home outside the land to a poor home in Eretz Yisrael. Even then, Rashi says, his wife cannot hold him back.

And no one can make the household leave Eretz Yisrael. This includes a slave who ran away from outside the land into Eretz Yisrael. Rabbeinu Gershom explains that his master cannot take him out again.

Everyone can make the household move up to Yerushalayim, even from a pleasant home to a poor one. Rabbeinu Gershom notes that life in a crowded city was counted as hard, as the Gemara says in Ketubot 110b.

And no one can make the household leave Yerushalayim. Who does that include? Even a move from a poor home to a pleasant one.

From here the Gemara turns to a second kind of "everyone": Mishnayot and baraitot that spell it out as Kohanim, Leviim and Yisraelim. Everyone is obligated in the mitzvah of sukkah: Kohanim, Leviim and Yisraelim.

The Gemara objects: isn’t that obvious?! If Kohanim, Leviim and Yisraelim are not obligated, who is?

It was needed for the Kohanim.

In Parshat Emor the Torah says "you shall dwell in sukkot," and our Sages teach that dwelling in the sukkah should be like living in a home. A home is where husband and wife live together, so the sukkah too is meant for husband and wife.

Kohanim, who serve in the Beit HaMikdash, cannot live that way. Rashi explains that the avodah of the Regel falls on them, so they keep apart from their wives. We might have thought they are exempt from sukkah.

So the Mishnah teaches: while they are doing the avodah they are exempt, and when they are not serving they are obligated.

It is like travelers. As a baraita in Sukkah 26a teaches, people on the road by day do not need a sukkah by day, but they do need one at night.

Everyone is obligated in the mitzvah of tzitzit: Kohanim, Leviim and Yisraelim. Again the Gemara objects: isn’t that obvious?!

It was needed for the Kohanim.

In Parshat Ki Teitzei the Torah writes "Do not wear shaatnez (wool and linen together)" right before "make tassels for yourself." From the two pesukim side by side we might learn that only one who is forbidden to wear kilayim, this mixture, is obligated in tzitzit.

Kohanim are allowed kilayim (with their bigdey kehunah), so we might have thought they are exempt from tzitzit.

The Mishnah teaches that kilayim is allowed to them only while they do the avodah. At other times it is forbidden to them too, so they are obligated in tzitzit. Rashi explains why kilayim is allowed in the avodah: the avnet, the Kohen's belt, was made of wool and linen, as the Torah describes it in Parshat Pekudei and the Gemara shows in Yoma 71b.

Everyone is obligated in the mitzvah of tefillin: Kohanim, Leviim and Yisraelim. Isn’t that obvious?!

It was needed for the Kohanim.

In Parshat Vaetchanan the Torah says "bind them as a sign upon your arm, and let them be totafot between your eyes." Both are in one pasuk, so we might say: whoever is obligated in the tefillin of the hand is obligated in the tefillin of the head.

Kohanim are not obligated in the tefillin of the hand while they serve. In Parshat Tzav the Torah says the Kohen puts his garment "on his flesh," so nothing may separate the garment from his body. Rashi explains that the tefillin of the hand sit on the upper arm, under the clothing, so they would be in between.

So we might say they are not obligated in the tefillin of the head either.

So the Mishnah teaches that the two tefillin do not depend on each other.

The Mishnah in Menachot 3 (on Menachot 38a) says it: the tefillin of the hand do not hold back the tefillin of the head, and the tefillin of the head do not hold back the hand. One who can put on only one of them puts on that one.

The Gemara asks: why is the hand different? Because the Torah wrote (he will wear it) "on his flesh"?

For the head, too, it is written, in Parshat Tetzaveh, "place the mitznefet (the turban) on his head." If the turban covers the head, where would the tefillin go?

A baraita answers; it is also on Zevachim 19a. The Kohen Gadol's hair showed between the tzitz, the gold plate on his forehead, and the mitznefet, and that is where he put his tefillin. Rashi explains that the turban sat high on the head and left open the place where a baby's skull is soft, which is the place of the tefillin.

Everyone is obligated in the mitzvah of shofar: Kohanim, Leviim and Yisraelim. Isn’t that obvious?!

It was needed for the Kohanim.

In Parshat Pinchas the Torah says "a day of teruah it will be for you." Rashi explains: a day, meaning one day only. So we might read it as: only one who blows on just one day of the year is obligated.

Kohanim blow all year long, as the Torah says in Parshat Behaalotcha: "you shall blow the chatzotzrot (trumpets) over your olot." So we might say they are not obligated in shofar.

The Gemara answers: how can the two compare? There the Kohanim blow trumpets; here it is a shofar.

Still, it was needed. We learned in the Mishnah in Rosh Hashanah 3 that Yovel is like Rosh Hashanah for the shofar blowing and for the berachot. Rashi explains that on Yom Kippur of the Yovel year they blew the shofar and said Malchiyot, Zichronot and Shofarot, as on Rosh Hashanah. So we might reason: whoever is part of the mitzvot of Yovel is part of the mitzvot of Rosh Hashanah, and whoever is not part of Yovel is not part of Rosh Hashanah.

And Kohanim are not part of the mitzvot of Yovel, as we learned in the Mishnah in Arachin 9 (on Arachin 33b): Kohanim and Leviim may sell their land at any time. Rashi explains that when a Yisrael sells a field in the Yovel year itself, the sale does not take hold and the money goes back (the Gemara teaches this on Arachin 29b). When a Kohen sells in that year, the sale takes hold and the money is his, though the field still returns to him at Yovel. Tosafot question this explanation and bring other readings.