Jesus stated in John 17:19:
“And for their sakes I sanctify Myself, that they also might be sanctified through the truth.”
First, some background. The word SANCTIFY means” To set apart for God’s use.” It really means to belong to God, which is why the word is often translated, “holy.” Likewise, the word SAINT comes from the same Greek word, “haggios,” and means, “holy ones, or ones set apart for God.” Indeed, even the term, “HOLY Spirit,” means, “the setting apart spirit.”
From this we see that to be holy or sanctified, is by definition, what a saved person IS unto God — by definition we belong to God through Christ.
But this must come to be more than just a fact. It is supposed to be manifested. Most of us have been taught that sanctification is a process whereby God acts upon us and makes us look holy, or to look like Jesus, or that sanctification it is something that we do — such as character building, keeping principles, acting happy, etc. But these are not the Truth.
According to Paul, Jesus Christ Himself in us — being manifested through us — IS sanctification. (I Cor. 1:30) “Jesus Christ is made to be unto us sanctification.” Note the distinction between the error of saying that we must look like Jesus, and the Truth that sanctification is Jesus Christ being manifested through us. (see below II Cor. 4) The difference is that of religion vs. LIFE.
We are sanctified by the Truth because if we are born from above, God is going to progressively reveal Christ in us — we will see Him, and because we see Him, we will more and more see the Truth. This will, in turn, set us free from all of the corruption of our minds by error — and in doing so — we will be sanctified by the Truth — we will KNOW God and realize the Truth of what it means to belong to Him.
Practically speaking, we will be able to live in the Truth of Christ. At the root, we will STOP belonging to ourselves — stop being preoccupied with fixing ourselves — and be set free to live from out of HIM. Thus, sanctification is both the process and the reality of Jesus Christ AS OUR LIFE — made possible by our death under the work of the Cross.
As for Jesus saying He sanctified Himself, He was referring to the fact that He was set apart to God for the purpose of Redemption — “I sanctify Myself, that they also might be sanctified through the Truth.” All that He accomplished as the Lamb of God made it possible, yes, for us to be saved, but also for us to belong to God IN HIM, and to be set free from the old creation into life in Him.
2 Corinthians 4(KJV)
4 Therefore seeing we have this ministry, as we have received mercy, we faint not;
2 But have renounced the hidden things of dishonesty, not walking in craftiness, nor handling the word of God deceitfully; but by manifestation of the truth commending ourselves to every man’s conscience in the sight of God.
3 But if our gospel be hid, it is hid to them that are lost:
4 In whom the god of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them.
5 For we preach not ourselves, but Christ Jesus the Lord; and ourselves your servants for Jesus’ sake.
6 For God, who commanded the light to shine out of darkness, hath shined in our hearts, to give the light of the knowledge of the glory of God in the face of Jesus Christ.
7 But we have this treasure in earthen vessels, that the excellency of the power may be of God, and not of us.
8 We are troubled on every side, yet not distressed; we are perplexed, but not in despair;
9 Persecuted, but not forsaken; cast down, but not destroyed;
10 Always bearing about in the body the dying of the Lord Jesus, that the life also of Jesus might be made manifest in our body.
11 For we which live are always delivered unto death for Jesus’ sake, that the life also of Jesus might be made manifest in our mortal flesh.
12 So then death worketh in us, but life in you.
13 We having the same spirit of faith, according as it is written, I believed, and therefore have I spoken; we also believe, and therefore speak;
14 Knowing that he which raised up the Lord Jesus shall raise up us also by Jesus, and shall present us with you.
15 For all things are for your sakes, that the abundant grace might through the thanksgiving of many redound to the glory of God.
16 For which cause we faint not; but though our outward man perish, yet the inward man is renewed day by day.
17 For our light affliction, which is but for a moment, worketh for us a far more exceeding and eternal weight of glory;
18 While we look not at the things which are seen, but at the things which are not seen: for the things which are seen are temporal; but the things which are not seen are eternal.