He is the one who will build it and receive the honor due a king, and he will rule his people. A priest will stand by his throne, and they will work together in peace and harmony.’
It was on the basis of the levitical priesthood that the Law was given to the people of Israel. Now, if the work of the levitical priests had been perfect, there would have been no need for a different kind of priest to appear, one who is in the priestly order of Melchizedek, not of Aaron.
But Jesus became a priest by means of a vow when God said to him, “The Lord has made a solemn promise and will not take it back: ‘You will be a priest forever.’”
The Law of Moses appoints men who are imperfect to be high priests; but God's promise made with the vow, which came later than the Law, appoints the Son, who has been made perfect forever.