How did Aharon and his sons know when to travel?
Rashi #1 and Seforno: When the Pillar of Cloud departed. 1
Rashi #2 (in Bamidbar 10:17) and Rashbam: The moment Yehudah began to travel, Aharon and his sons entered the Mishkan and took down the Paroches and covered the Aron with it 2 (and also the other holy vessels, as the Pasuk goes on relate).
Seforno; Before which they were forbidden to enter the Ohel Mo?ed.
Rashi (ibid.): As the Torah writes here "And Aharon and his sons shall come ... ". The B'nei Gershon and B'nei Merari then came and dismantled the Mishkan and loaded it on to the wagons, and the Aron and the Holy vessels, which the B'nei K'has would carry, remained standing covered, in their place, attached to poles, until Degel Machaneh Reuven traveled, at which point the B'nei K'has traveled (carrying the holy vessels on their shoulders).
Why was it necessary for Aharon and his sons to cover the holy vessels in advance? Why could the B'nei K'has not do it when they came to carry them?
Rashi (in Pasuk 15): To avoid the B'nei K'has dying at the Hand of Hashem, by inadvertently touching the holy vessels, as the Torah indicates in Pasuk 18 & 19.
Yerushalmi (in Bikurim, 2:1): To avoid the B'nei K'has dying at the Hand of Hashem by deriving pleasure from gazing at the Kodesh Kodshim.
