The people were given the law concerning the system of priests from the tribe of Levi, but they could not be made perfect through that system. So there was a need for another priest to come, a priest like Melchizedek, not Aaron.
No one knows who Melchizedek’s father or mother was, where he came from, when he was born, or when he died. Melchizedek is like the Son of God; he continues being a priest forever.
Priests receive a tenth, even though they are only men who live and then die. But Melchizedek, who received a tenth from Abraham, continues living, as the Scripture says.