Leviticus 21:15

Neither shall he profane his seed among his people: for I the LORD do sanctify him.

The command belongs to the wider instruction in Leviticus 21:6-23 laying down the standard for those who served in the sanctuary. They were required to be pure and holy in life and character. The reason was that their work brought them into close connection with God. God has not changed in holiness and particularity, so those who minister for Jesus are under the same obligation to be pure and without blemish. Their daily life must reflect the sacredness of their calling.