Hebrews 7:4-6, 9-12

You can see how great Melchizedek was. Abraham, the great father, gave him a tenth of everything that he won in battle. Now the law says that those in the tribe of Levi who become priests must collect a tenth from the people—their own people—even though the priests and the people are from the family of Abraham. Melchizedek was not from the tribe of Levi, but he collected a tenth from Abraham. And he blessed Abraham, the man who had God’s promises.

We might even say that Levi, who receives a tenth, also paid it when Abraham paid Melchizedek a tenth. Levi was not yet born, but he was in the body of his ancestor when Melchizedek met Abraham. 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. And when a different kind of priest comes, the law must be changed, too.