Born of the Spirit

Being in sin is walking in your flesh. The opposite of being in the flesh is being in the Holy Spirit. If you have been freed from sin, you’re free to walk in the Holy Spirit.

But I say, walk by the Spirit, and you will not carry out the desire of the flesh. For the flesh sets its desire against the Spirit, and the Spirit against the flesh; for these are in opposition to one another, so that you may not do the things that you please. But if you are led by the Spirit, you are not under the Law. Now the deeds of the flesh are evident, which are: immorality, impurity, sensuality, idolatry, sorcery, enmities, strife, jealousy, outbursts of anger, disputes, dissensions, factions, envying, drunkenness, carousing, and things like these, of which I forewarn you, just as I have forewarned you, that those who practice such things will not inherit the kingdom of God. (Galatians 5:16-21)

Leaving behind the Law and sin is called sanctification. Sanctification is becoming righteous and holy by the supernatural power of the Holy Spirit.

...to be a minister of Christ Jesus to the Gentiles, ministering as a priest the gospel of God, so that my offering of the Gentiles may become acceptable, sanctified by the Holy Spirit. (Romans 15:16)

when you present yourselves to someone as slaves for obedience, you are slaves of the one whom you obey, either of sin resulting in death, or of obedience resulting in righteousness? But thanks be to God that though you were slaves of sin, you became obedient from the heart to that form of teaching to which you were committed, and having been freed from sin, you became slaves of righteousness. I am speaking in human terms because of the weakness of your flesh. For just as you presented your members as slaves to impurity and to lawlessness, resulting in further lawlessness, so now present your members as slaves to righteousness, resulting in sanctification. (Romans 6:16-19)

...by the sanctifying work of the Spirit...  (1 Peter 1:2)

But many Christians don’t believe Jesus actually does free you from flesh and sin. Because of their lack of faith, they continue to struggle with sin. This struggle is usually justified by teaching that sanctification is a lifelong process. If sanctification is a lifelong process, there is still room for some sin in the life of a believer. It gives a Christian permission to rely on himself to become righteous over time by his own effort, and permission to fail on his own effort, rather than relying on the supernatural power of God through the Holy Spirit.
 
However, this is not at all what scripture teaches. Nowhere does the Bible give any indication that sanctification takes a long time. In fact, Paul tells the Roman church they’ve already been sanctified:

But now having been freed from sin and enslaved to God, you derive your benefit, resulting in sanctification, and the outcome, eternal life. (Romans 6:22)

And sanctification is part of salvation.

Salvation through sanctification by the Spirit and faith in the truth. (2 Thessalonians 2:13)

The Holy Spirit doesn’t just sanctify us. We are unified to Jesus by the Holy Spirit.

Both He who sanctifies and those who are sanctified are all from one Father; for which reason He is not ashamed to call them brethren. (Hebrews 2:11)

But God, being rich in mercy, because of His great love with which He loved us... made us alive together with Christ (by grace you have been saved), and raised us up with Him, and seated us with Him in the heavenly places in Christ Jesus... For we are His workmanship, created in Christ Jesus for good works... through Him we both have our access in one Spirit to the Father. Christ Jesus Himself being the corner stone, in whom the whole building, being fitted together, is growing into a holy temple in the Lord, in whom you also are being built together into a dwelling of God in the Spirit. (Ephesians 2:4-6, 10, 20, 21-22)

For you have not received a spirit of slavery leading to fear again, but you have received a spirit of adoption as sons by which we cry out, “Abba! Father!” (Romans 8:15)

Through the Holy Spirit, we have been adopted into the righteous family of God!