Leviticus 21:5
They shall not make baldness upon their head, neither shall they shave off the corner of their beard, nor make any cuttings in their flesh. They shall not make baldness upon their head, neither shall they shave off the corner of their beard, nor make any cuttings in their flesh.
Leviticus 21:5 stands within Leviticus 21-23, which deals largely with laws relating to sacrifices and offerings, the consecration and duties of the priests, and the various feasts of the year. It forbids priests to make baldness upon the head, to shave off the corner of the beard, or to make cuttings in the flesh as an outward show of mourning or defiling custom for the dead, with exception only for immediate family. In the death of Nadab and Abihu even that family exception was removed because the offense was so heinous. Aaron and his remaining sons had to fully acquiesce in God's judgment with no sign of dissent, and could not follow the bodies out or attend the funeral. Relatives outside the priesthood had to dispose of the dead priests, who were buried in their polluted priestly robes.
The shaving of the head and trimming of the corners of the beard are forbidden because the heathen priests did those things and God's priests must not seem to be like them. The command was given while Israel was surrounded by nations sunken in the grossest idolatry with many degenerate Canaanites still remaining in the land. Like many other customs it was prohibited for the sole reason that it was a heathen custom. Cutting or shaving the body for fashion defaces it and is inconsistent with the holiness required of a sacrifice offered to God. Like each detail of all these sacrifices, this command had its meaning, and its fuller meaning is found in the sacrifice, life, and work of Jesus Christ.