Jamieson, Fausset and Brown on Leviticus 7:35-38

35-38. This is the portion of the anointing of Aaron--These verses contain a general summing up of the laws which regulate the privileges and duties of the priests. The word "anointing" is often used as synonymous with "office" or "dignity." So that the "portion of the anointing of Aaron" probably means the provision made for the maintenance of the high priest and the numerous body of functionaries which composed the sacerdotal order.

in the day when he presented them to minister unto the Lord, &c.--that is, from the day they approached the Lord in the duties of their ministry.