Leviticus 21 turns to those who served closest to God's presence. The priests, Aaron's sons, offered the offerings of Yahweh made by fire, the bread of their God. Therefore they shall be holy to their God. Their mourning practices, their marriages, and their families were all to reflect the holiness of their calling. Israel was to treat them as holy, for I Yahweh, who sanctify you, am holy.
The high priest stood under even stricter rules. He could not uncover his head, tear his clothes, or go near any dead body, even for his father or mother, and he was not to leave the sanctuary in mourning. The crown of the anointing oil was on him. He was to marry an Israelite virgin, so that his offspring would not be profaned.
Verses 17 to 23 state that no descendant of Aaron with a physical defect could approach the altar to offer. This did not mean such a man was less valuable; the altar service was a visual picture of the perfect holiness required to approach God. Verse 22 is gracious: He shall eat the bread of his God, both of the most holy, and of the holy. He remained in the priestly family and shared its food. In Christ, the perfect High Priest without blemish (Hebrews 7:26), all who believe are welcomed, and Jesus healed the blind and lame who came to Him in the temple (Matthew 21:14).