<p>7:5 <i>And they indeed of the sons of Levi that receive the priest's office- </i>Paul doesn't call them Aaronites because he wants to make the point that the tribal head, Levi, was not the ancestor of Melchizedek; and as one of the patriarchs, he as it were paid tithes in Abraham to Melchizedek.</p><p><i>Have the commandment according to the law to take tithes from the people, that is, of their brothers; even though they are also descendants of Abraham</i>- Levi's sons could take tithes of their brothers, but this did not make them 'greater' than their brothers. They were 'brothers' on the same level as those who tithed to them. But payment of tithes to an unrelated person was a more impressive evidence of the greatness of that person over the tithe payers.</p>