Hebrews 5:4

And no man taketh this honour unto himself, but he that is called of God, as was Aaron.

The honor is the high priesthood, which no one takes for himself but receives only by being called by God, just as Aaron was called. No position or authority gives a person even the smallest favor with God. The high priest is taken from among men and ordained to act for men in things relating to God, offering gifts and sacrifices for sins. He can have compassion on the ignorant and on those out of the way because he himself is beset with weakness, and he must offer for his own sins as well as for the sins of the people.

Christ did not glorify Himself to become High Priest but was called, appointed, and set apart by God, who declared Him to be His Son and to be a priest forever after the order of Melchizedek. Taken from among men in human nature, bone of bone and flesh of flesh, He is the chosen Mediator, the only begotten Son who knew no sin and bore the penalty of sin. He alone could approach God in humanity with hope. He fulfills this compassionate priesthood as one tempted in every way as human beings are yet without sin, who in the days of His flesh offered prayers and supplications with strong crying and tears to Him who was able to save Him from death, learned obedience through the things He suffered, was made perfect, and became the author of eternal salvation to all who obey Him. By His divine appointment and perfect character He is the true High Priest, the representative and Advocate for humanity.

Through Him alone repentant sinners are accepted in the Beloved, received by the Father, clothed with the robe of righteousness, made obedient sons and daughters and members of the royal family, and given eternal life. Therefore tried and tempted people can come boldly to the throne of grace to obtain mercy and find grace for help in time of need, and no man can sever them from Him. His priestly calling was for service to others, not for self-glorification.

The same principle applies to the work of a prophet, for the prophets through whom God spoke in former times were men specially chosen and qualified by Him for the sacred office of revealing His will, given special light and commanded to tell the people what He directed them to speak. The same principle applies to the sacred work of the ministry, which is not taken by oneself but comes by God's call, so a candidate for ordination should give evidence of personal conviction that God has called him. The verse points to a God-given calling rather than self-exaltation, and in connection with reading the surrounding chapters it confronts envy, suspicion, and accusation.