Charles Ellicott Commentary Leviticus 21:12

"neither shall he go out of the sanctuary, nor profane the sanctuary of his God; for the crown of the anointing oil of his God is upon him: I am Jehovah." — Leviticus 21:12 (ASV)

Neither shall he go out of the sanctuary. —Better, and he shall not go out of the sanctuary as in Leviticus 10:7. When the news of a parent's death is brought to him during the service, he must not cease the service and leave the sanctuary, lest he appear to have greater regard for the dead than for the service of the living God.

The difference between the ordinary priest and the high priest in this respect was, that when the former heard, during the service, of the death of any one of the seven relations for whom he had to mourn, he was obliged to discontinue the service, though he too could not leave the precincts of the sanctuary; while the latter, under these circumstances, was bound to continue the service. The former, by becoming a mourner, profaned the service if he continued it; the latter never became a mourner, and hence profaned the service if he discontinued it.