The word Sanctification simply means Holiness. To sanctify, is to separate or to set apart something as Holy.
Compare these versions.
John 17:17 (WEB) Sanctify them in your truth. Your word is truth.
John 17:17 (NET) Set them apart in the truth; your word is truth.
John 17:17 (BBE) Make them holy by the true word: your word is the true word.
Sanctification happens in two phases.
1. When you are born again, you are washed clean by the blood of Jesus, making you holy and set apart for the gospel.
Hebrews 13:12 (WEB) Therefore Jesus also, that he might sanctify the people through his own blood, suffered outside of the gate.
By virtue of the blood of Jesus you were made Holy when you believed.
Hebrews 10:29 (WEB) How much worse punishment do you think he will be judged worthy of who has trodden under foot the Son of God, and has counted the blood of the covenant with which he was sanctified an unholy thing, and has insulted the Spirit of grace?
After we have been made Holy we are placed in the world, and we are commanded to separate ourselves from the lusts of the world. We are to be Holy. To sanctify ourselves by not partaking in things that defile.
2 Timothy 2:21-22 (WEB)
21 If anyone therefore purges himself from these, he will be a vessel for honor, sanctified, and suitable for the master’s use, prepared for every good work.
22 Flee from youthful lusts; but pursue righteousness, faith, love, and peace with those who call on the Lord out of a pure heart.
1 Peter 1:15-16 (WEB)
15 but just as he who called you is holy, you yourselves also be holy in all of your behavior;
16 because it is written, “You shall be holy; for I am holy.”
This second phase can not be achieved by human efforts. Its achieved by faith, through the word of God, and guidance of the Holy Spirit. When you are born again, your spirit is regenerated. You new spirit will naturally have a connection with the things of God, and will naturally feel disconnected to the things of the world. This becomes stronger as you mature.
You also receive the Holy Spirit in you. Who empowers you to subdue the desires of the flesh.
Romans 8:9-11 (NET)
9 You, however, are not in the flesh but in the Spirit, if indeed the Spirit of God lives in you. Now if anyone does not have the Spirit of Christ, this person does not belong to him.
10 But if Christ is in you, your body is dead because of sin, but the Spirit is your life because of righteousness.
11 Moreover if the Spirit of the one who raised Jesus from the dead lives in you, the one who raised Christ from the dead will also make your mortal bodies alive through his Spirit who lives in you.