Therefore you and your sons with you shall keep your priest's office for everything at the altar, and within the veil; and you shall serve: I have given your priest's office unto you as a gift for service: and the stranger that comes near shall be put to death.
Read Chapter 18
George Leo Haydock
Priests. Hebrew, "you shall serve in the ministry of priests which I have given you. "The office was not due to them on account of any superior merit. (Haydock)