Albert Barnes Commentary Hebrews 7:5

"And they indeed of the sons of Levi that receive the priest`s office have commandment to take tithes of the people according to the law, that is, of their brethren, though these have come out of the loins of Abraham:" — Hebrews 7:5 (ASV)

And truly those who are of the sons of Levi. The meaning of this verse is that the Levitical priests had a right to receive tithes from their brothers, but still they were inferior to Melchizedek. The apostle admits that their superiority to the rest of the people was shown by the fact that they had a right to require from them the tenth part of the produce of the land for their maintenance and for the support of religion. But still he says that their inferiority to Melchizedek, and consequently to Christ as a priest, was shown by the fact that the illustrious ancestor of all the Jewish people, including the priests as well as others, had confessed his inferiority to Melchizedek by paying him tithes.

Who receive the office of the priesthood. Not all the descendants of Levi were priests. The apostle, therefore, specifies particularly those who received this office, as being those he particularly intended to discuss, and as those whose inferiority to Christ as a priest his object was to show.

Have a commandment to take tithes. By the law, they have a commission or a right to exact tithes from the people (Deuteronomy 14:22, 27-29).