According to the covenant made with David son of Jesse, of the tribe of Juda, that the inheritance of the king should be to his posterity alone: so the inheritance of Aaron should also be to his seed.
Read Chapter 45
In a mysterious sense, it is right that the dignity of the eternal priesthood is promised to Phinehas, son of Eleazar the priest, for the zeal that he had against the fornicators. Indeed, whoever, moved by godly zeal, makes an effort to suppress the impulses of his flesh or reproves and restrains those under him, so as to not let them deviate from the truth out of lust and sexual desire, will have the dignity of the eternal priesthood in the church of God, which rightly belongs to that priest of whom it is written, "Like Melchizedek, you are a priest forever." He will possess, with him, the eternal kingdom in heavenly light. - "On Ecclesiasticus 10.10"