Leviticus 1:6

Flay the burnt offering. Originally, the offerer himself did this, though this part of the ritual was later taken over by the Levites. In the wilderness there were but few to participate in the services, as compared with later times, in the Promised Land, when hundreds and even thousands of offerers arrived in a single day. The Levites and priests who were accustomed to the ritual could perform the flaying more expeditiously than the people.