5:4 Nobody takes this honor on himself, but he is called by God, just like Aaron was.
The false religions of the day appointed to priesthood anyone they pleased; and in fact the Jewish priesthood had itself declined to that point, with the High Priest being a secular appointment. That, however, was not the Lord’s original intention. When the people of Israel rejected God’s call to be a nation of priests, He appointed a single tribe, the Levites, as the one from which all priests would come. He then went further and appointed a single family, that of Aaron. The High Priests were to be chosen, not for any personal quality, but for their position in that family. They were part of that family because of God’s grace – it was impossible for them to have done anything to have merited being born into the line of Aaron. Thus the Old Testament priesthood foreshadowed the New Testament call to ministry, which is based not on the merits, abilities or qualifications of the individual, but on God’s grace.
Whilst the Old Testament priest could not merit his position, neither could he choose it for himself. One who was not of the family of Aaron could not simply decide to become a High Priest. The choice was completely in the hands of the Lord.
New Testament ministry is not based on family lines and inheritance, as was the Old Testament priesthood, but on a spiritual call. Nonetheless, the appointment is totally from God. No man or woman can call himself or herself to ministry. Neither can any individual, or even the church as a body, call another person to ministry. The most we can do is to recognize the call that God has already placed on the individual’s life.
That, however, is not the writer’s point here. Rather, he is demonstrating that, just as the priests of the Old Covenant held their office purely by the call of God, so did Christ.
5. So also Christ didn’t glorify himself to be made a high priest, but it was he who said to him,
“You are my Son. Today I have become your father.” (6) As he says also in another place, “You are a priest forever, after the order of Melchizedek.”
Aaron’s appointment as High Priest came directly from the Lord. For those who followed him in the office, their appointment came from God through the fact that He had caused them to be born into the family of Aaron. Christ, however, was not appointed because of His human lineage, but by a direct word from the Father. His appointment was a result of His relationship with the Father, not his natural family.
Here the writer takes the opportunity to introduce a new theme. Not only is Christ’s priesthood better than that of the Old Covenant priests, it is of an entirely different nature. He will go on in subsequent chapters to expand upon both the specifics of the Melchisedeck priesthood and the differences between it and the Aaronic priesthood.