Bamidbar

The book of Bamidbar opens with a census of all the males over twenty, the age when they are able to serve in the army. The total, excluding the tribe of Levi who were not counted, was 603,550. The Levi'im are placed in charge of carrying the Mishkan (Tabernacle) and all of its fittings throughout the journeys in the desert. G-d designates each tribe's place surrounding the Mishkan in which they will remain during their time in the desert. Yehuda, Yissachar and Zevulun shall be to the East; Reuven, Shimon and Gad are placed in the south; Ephraim, Menashe and Binyamin to the West; and Dan, Asher and Naftali in the North.
The Torah lists Aaron's genealogy. The Levi'im are instructed to safeguard the Mishkan, and to serve the Cohanim. The tribe of Levi is given the honour of looking after the Mishkan in lieu of the firstborn who were originally intended for the position. The Levi'im are subdivided into three family groupings and a census of their numbers taken, from the age of one month upward. Their total number is 22,000. The tally of firstborn males is 22,273. The firstborn are exchanged for Levi'im, and the remaining 273 firstborn have to redeem themselves for five shekels each. This money is given to the Cohanim.
Special instructions and precautions are given to the family of Kehat who are the ones who have to carry the vessels of the Mishkan. First the Cohanim must enter the Mishkan and cover all of the furnishings with special covers; only when they have completed this may the Kahatites come to carry them. Because they are in contact with the most holy parts of the Mishkan, they are most at risk of being killed if they don't perform their task properly.