2. Speak unto Aaron and to his sons, that they separate themselves from the holy things--"To separate" means, in the language of the Mosaic ritual, "to abstain"; and therefore the import of this injunction is that the priests should abstain from eating that part of the sacrifices which, though belonging to their order, was to be partaken of only by such of them as were free from legal impurities.
      that they profane not my holy name in those things which they hallow unto me, &c.--that is, let them not, by their want of due reverence, give occasion to profane my holy name. A careless or irreverent use of things consecrated to God tends to dishonor the name and bring disrespect on the worship of God.

JFB.