Why does the Torah write "Venas'u ha'Kehasim (plural) Nos'ei ha'Mikdash"?
Menachos, 94b: "Venas'u ha'K'hasim" implies 'two' and so "Nos'ei ha'Mikdash" - to teach us that four people carried the Aron.
Why does the Torah insert the (otherwise superfluous) words "Venas?u ha?Kehasi Nos'ei ha'Mikdash"?
Yerushalmi Eruvin, 5a: "ha'Mikdash" refers to the Aron and the Torah inserts it here to teach us that the Aron would indicate to them the directions - north, south, east and west (to mark the llocations that the the four Degalim encamped) - by placing itself east to west. 1
This means that, when the Cloud stopped travelimg, the B'nei Gershon and the B'nei Merari could not erect the Mishkan before the B'nei K'has arrived with the Aron.
Who set up the Mishkan before the B'nei K'has arrived?
Rashi: The B'nei Gershon and Merari (who dismantled the Mishkan, and) who traveled two Machanos 1 ahead of the B'nei K'has, set up the Mishkan, so that, when the B'nei K'has arrived, they would be able to arrange the holy Keilim in their places immediately. 2
Refer to 10:21:151:1 & 2.
See Oznayim la'Torah DH 'Ve'heikimu es ha'Mishkan' #2, who queries Rashi from the Yerushalmi - Refer to 10:21:2:1* and explains why Rashi declines to explain the Pasuk accordingly.
Rashi (2:17) writes that the Mishkan traveled after two Machanos. But here the Torah writes that only Degel Yehudah traveled before the Mishkan?
Refer to 2:17:2:4.
QUESTIONS ON RASHI
Rashi writes that the B'nei Gershon and Merari traveled two Machanos before the B'nei K'has. But only Degel Reuven traveled between them?
Mizrachi: "Vayisa? Yehudah" (Pasuk 14) means that they prepared to travel, but they did not actually travel until the B'nei Gershon and Merari dismantled the Mishkan 1 and loaded it on the wagons. Gur Aryeh ? it would be disrespectful for them to travel while the Mishkan was in its place.
Oznayim la'Torah: What Rashi means is that, according to he opinion that they traveled in a straight line, Reuven had to travel twice - first from their southern position towards the east in order to get into line behind the B'nei Gershon and Merari, and then to begin following, them. Hence Rashi writes (not 'she'Hayu Kodmin lahem 'Sh'nei Degalim', but) ' ... Masa Sh'nei Degalim'.
Rashi wrote (Pasuk 17) that they dismantled the Mishkan only after Yehudah traveled! (PF)
