Which tribe did all Israelite priests have to come from?
All Israelite priests had to come from the tribe of Levi. Beginning with Aaron as the first high priest, no one could serve as a priest unless they were of Levi. The Levitical priesthood was therefore the required lineage for Israel's priests.
Les teaches that the priesthood of Israel began with Aaron, the very first high priest, way back before they came out of Egypt. Every priest had to come from the tribe of Levi; they could not be a priest unless they were of Levi, and Aaron was the first one. This is the Levitical priesthood mentioned in verse 11 of chapter 7. Les contrasts it with Melchizedek, whom he maintains was Jehovah, or God the Son, in a theophany—God appearing in human form to Abraham. Since Melchizedek had no genealogy, no beginning or ending, Les feels it was Christ appearing to Abraham to lay the groundwork for our high priest, for us as Gentiles, a high priest not tied to the law of Israel.
If therefore perfection were by the Levitical priesthood, (for under it the people received the law,) what further need was there that another priest should rise after the order of Melchisedec, and not be called after the order of Aaron?