Hebrews 5:4-5 (ESV)
And no one takes this honor for himself, but only when called by God, just as Aaron was.
 So also Christ did not exalt himself to be made a high priest, but was appointed by him who said to him,
“You are my Son,
today I have begotten you”;
What is the relationship between the appointment of Jesus as high priest and His sonship? This text says that Jesus did not take the honour of the priesthood upon Himself but He was appointed to it by the one who said “You are my Son. Today I have begotten you.”
Does this mean that before Jesus was appointed as high priest he was not the begotten Son? The Scriptures will not allow that. Can we ever speak of a “time” when Jesus was not appointed to be high priest? The relationship between Jesus sonship and His appointment as high priest is that in becoming high priest Jesus is not grabbing something that is too lofty for Him.
Someone could argue that Jesus didn’t have the right to be high priest since He was not from the priestly tribe of Levi. “Quite right”, the writer to the Hebrew believers says. He is not a Levite. He is the Son of God. Christ was not exalting Himself when He took the office of eternal high priest. He is not stepping up. He is stepping down. He is the eternal King that the quoted Old Testament passage talks about. He is a priest, not by virtue of His tribal heritage, but because of His being a priest like Melchizedek. (More on him some other time).
When Christ became the great high priest that we need in order to be eternally forgiven, He was being obedient to His Father. He was not exalting Himself, He was submitting Himself to the will of the Father. Can we just stop there and think about that as it relates to our obedience?
How often do we grumble about what God’s standards are? How often do we wish that pre-marital sex wasn’t wrong, or that wasting hours of time in front of games and TV and general mindlessness was all commanded by God? How often do we simply choose to do what we want instead of what God tells us? As the Son of God, the second Person of the trinity obeyed the will of His eternal Father by “making Himself nothing, and becoming obedient to death…”.
You have commandments from God that are too difficult? You are hard done by, by the God you have been called to serve? God has given you things to do that are below you?? All these attitudes melt away before the Christ who was appointed and willingly came to earth to die for sinners. How dare we say that God is being unfair. There can be nothing more unfair than the sinless Son of God taking the punishment for a vast numberless host of people who were happy to run away from Him, who did not deserve to be sought after, and who do deserve eternal punishment. The Gospel is stunning. And those who really have it will live their lives in joyful service to Him and others, no matter who they are and what it takes.