This statement of our LORD Jesus Christ sanctifying Himself is drawn from the Old Testament imagery of priests being sanctified (set apart) unto God for the work of the ministry on behalf of the people. Priests were to be hallowed (sanctified) by God for the work of representing the people, Leviticus 11. Sacrifices were consecrated (sanctified) according to the requirements of the law for God to be forbearing with their sin, Lev. 4.
In the work of sanctification of the LORD Jesus we find two key elements. How He sanctified Himself and those for whom He sanctified Himself.
1.) How the LORD Jesus sanctified Himself. As God’s appointed High Priest, He was eternally sanctified (set apart to this work) by God the Father, Isaiah 42:1; Matthew 12:18. Therefore, the LORD Jesus as God in the flesh sanctified Himself in willing submission to His Father. He set Himself apart to fully satisfy God the Father’s law and justice that by His sanctification, His people would also be sanctified in Him, John 17:17. The high priests of the Old Testament went into the sanctuary bearing the names of their people on their breastplates, Exodus 28:12,29. Even so the LORD Jesus Christ came to earn and establish God the Father’s righteousness in His life and then to lay down His life so that the whole of His life and death, as God’s High Priest, was the complete satisfaction of the Father for His elect.
2.) Those for whom He sanctified Himself. ‘For their sakes,’was not for everybody in the world as John 17:2 declares. Christ did NOT pray for the world but for those that the Father gave Him from out of the world. He died for a world of sinners that the Father purposed should be sanctified (set apart) in His work as their Substitute. When Christ prayed ‘for their sakes,’ the word ‘for’ means, ‘on behalf of’ or ‘in the place of’ another. Many falsely presume that sanctification is their work but clearly, from Christ’s intercessory prayer here, it was His work to do on behalf of those that the Father gave Him.
What about the Scripture that says,“Sanctify yourselves therefore, and be ye holy: for I am the LORD your God.”(Leviticus 20:7)? In the Old Testament this was a commandment for the people to set themselves apart to submit to the high priests and the sacrifices being offered on their behalf. However, in the New Testament, we are not instructed to sanctify ourselves as if we have anything to offer. All the sanctification (being set apart by God in Christ) was accomplished by Christ by Him sanctifying Himself on our behalf. And it is God, by His Spirit that continues to keep His elect, redeemed and justified children in that state of sanctification unto Him, by the righteousness imputed of the LORD Jesus at the cross, 1 Peter 1:2.
1 Thessalonians 5:23 states, “And the very God of peace sanctify [literally, continue to sanctify] you wholly; and I pray God your whole spirit and soul and body be preserved [kept] blameless [in Christ’s cross work] unto the coming of our LORD Jesus Christ.” Sanctification is the work of God the Father, God the Son and God the Holy Spirit.
-God the Father sanctified sinners in His election of them (setting them apart in Christ), John 17:17.
-God the Son sanctified them in His death on the cross, Ephesians 5:26.
-God the Spirit sanctifies them in calling them to Christ (separating them out in regeneration from Spiritual death and darkness), 2 Cor. 3:18.
This is God’s work “for their sakes,” each one that HE has purposed to save and has saved and justified in the death of His Son, 1 Corinthians 1:30; “Being confident of this very thing, that he which hath begun a good work in you will perform it until the day of Jesus Christ.” (Philippians 1:6)