1) MOVING THE WAGONS OF THE MISHKAN
QUESTION: The Mishnah says that one is forbidden to pass an object from a Reshus ha'Yachid to another Reshus ha'Yachid via Reshus ha'Rabim ("Moshit"). RASHI explains that this is derived from the way in which the wagons were loaded when the Mishkan was dismantled in preparation for the Jewish people to continue their travels in the desert. Two wagons were stationed next to each other, and in front of them was another pair of wagons. The Leviyim would pass the pillars (Kerashim) of the Mishkan to the first pair of wagons, and Leviyim on those wagons would take the pillars and pass them on to the second pair of wagons to be loaded there.
Why did they load the wagons in such an unusual way? It is logical that they loaded only two wagons at a time, since they traveled in the desert with two wagons next to each other (99a). However, they should have simply filled up the first two wagons and then moved them out of the way, brought the other two wagons into position and loaded them with pillars. Why did they pass the pillars to the first wagon and then to the second?
(a) Perhaps it was not respectful to require the second set of pillars to wait while the wagons moved out of the way with the first set.
(b) Whenever the Mishkan and the Jewish people traveled, they had to follow the lead of the Ananei ha'Kavod, the Clouds of Glory, and the call of the Chatzotros. If the first set of wagons would be loaded with pillars and then moved in order to bring the second set of wagons into the loading position, then when they would start to move it out of the way, that movement would be considered the start of their journey. Since it was forbidden to begin traveling until the Ananei ha'Kavod started to move and the Chatzotros sounded, they could not move the wagons. They had to pass the pillars over the first wagon and into the second. (M. KORNFELD)
2) THE SOURCE FOR THE MELACHAH OF "HOTZA'AH"
QUESTION: The Gemara asks where the Melachah of Hotza'ah is mentioned in the Torah. Why does the Gemara search for a verse for the Melachah of Hotza'ah? The Gemara earlier (49b) states that Hotza'ah was done in the Mishkan, and any Melachah that was done in the Mishkan is prohibited to do on Shabbos.
ANSWER: TOSFOS (DH Hotza'ah) explains that Hotza'ah is a Melachah Geru'ah, a "weaker" Melachah. (This is because Hotza'ah does not change the object upon which it is done. Alternatively, it is because the domains of Shabbos are Halachic and not physical entities. See Insights to Shabbos 1:1.) Therefore, a verse is necessary to teach that Hotza'ah indeed is prohibited on Shabbos.
3) A "TOLDAH" OF "HOTZA'AH"
QUESTION: The Gemara teaches that Ma'avir and Zerikah (carrying and throwing an object four Amos in Reshus ha'Rabim) are Toldos of the Melachah of Hotza'ah. Why are they Toldos of Hotza'ah? In what way is transporting an object a distance of four Amos in Reshus ha'Rabim similar to taking an object from Reshus ha'Yachid to Reshus ha'Rabim?
ANSWER: The BA'AL HA'ME'OR (see also TOSFOS HA'ROSH) explains that a "person's place" is four Amos. That is, the area of four Amos around the point where a person stands is considered to be "his" area (Bava Metzia 10a). When one carries the object from the place in which he stands, he thereby takes it into a "new" Reshus, so to speak. Accordingly, when one carries four Amos in Reshus ha'Rabim, it is as if he carries from one Reshus to another Reshus.