John Gill Commentary Leviticus 21:8

"Thou shalt sanctify him therefore; for he offereth the bread of thy God: he shall be holy unto thee: for I Jehovah, who sanctify you, am holy." — Leviticus 21:8 (ASV)

You shall sanctify him therefore In thought and word, as Aben Ezra, by thinking and speaking well of him; should esteem and reckon him a holy person, being in a sacred office, and honour him as such; and do all that can be done to preserve him from unholiness and impurity, and particularly from marrying with improper and unsuitable persons, such as would bring a scandal on him and his sacred office: this seems to be spoken to Moses, and so to the civil magistrate in succession, who were not to suffer such marriages to take place in the priesthood; and were not only to persuade from it, but to exercise their authority, and oblige them to put away such wives, and if they refused, to use severity; so Jarchi, ``"you shall sanctify him", whether he will or not; if he will not put her away, beat him and chastise him until he does put "her away",'' see (Ezra 2:62);

for he offers the bread of the Lord meaning not the shewbread he set in order before the Lord every week, but the various gift and sacrifices which were offered to God by him, and were acceptable to him as his food; and therefore he ought to be holy that drew nigh to God, and was employed in such service, see (Leviticus 21:6);

he shall be holy to you in your account and estimation, and for your service to offer holy sacrifices, and therefore should be careful of his holiness to preserve it:

for I the Lord, who sanctify you, [am] holy in his nature, works, and ways, and who had separated them from all other people to be a holy people to him, and therefore they that ministered in holy things for them should be holy likewise.