Hebrews 7:4

4.Now consider, etc. This is the fourth comparison between Christ and Melchisedec, that Abraham presented tithes to him. But though tithes were instituted for several reasons, yet the Apostle here refers only to what serves his present purpose. One reason why tithes were paid to the Levites was, because they were the children of Abraham, to whose seed the land was promised. It was, then, by a hereditary right that a portion of the land was allotted to them; for as they were not allowed to possess land, a compensation was made to them in tithes. There was also another reason, — that as they were occupied in the service of God and the public ministry of the Church, it was right that they should be supported at the public cost of the people. Then the rest of the Israelites owed them tithes as a remuneration for their work. But these reasons bear not at all on the present subject; therefore, the Apostle passes them by. The only reason now alleged is, that as the people offered the tithes as a sacred tribute to God, the Levites only received them. It hence appears that it was no small honor that God in a manner substituted them for himself. Then Abraham, being one of the chief sergeants of God and a prophet, having offered tithes to Melchisedec the priest, thereby confessed that Melchisedec excelled him in dignity. If, then, the patriarch Abraham owned him more honourable than himself, his dignity must have been singular and extraordinary. The word patriarch is mentioned for the sake of setting forth his dignity; for it was in the highest degree honourable to him to have been called a father in the Church of God.

Then the argument is this, — Abraham, who excelled all others, was yet inferior to Melchisedec; then Melchisedec had the highest place of honor, and is to be regarded as superior to all the sons of Levi. The first part is proved, for what Abraham owed to God he gave to Melchisedec: then by paying him the tenth he confessed himself to be inferior.