What is Christian Sanctification?

“Sanctification” is a translation of the Greek word hagiasmos, meaning “holiness” or “a separation.” In the past, God granted us justification, a once-for-all, positional holiness in Christ. Now, God guides us to maturity, a practical, progressive holiness. In the future, God will give us glorification, a permanent, ultimate holiness. These three phases of sanctification separate the believer from the penalty of sin (justification), the power of sin (maturity), and the presence of sin (glorification).

John 17:14-21

14 I have given them thy word; and the world hath
hated them, because they are not of the world, even
as I am not of the world.
15 I pray not that thou shouldest take them out of
the world, but that thou shouldest keep them from
the evil.
16 They are not of the world, even as I am not of
the world.
17 Sanctify them through thy truth: thy word is
truth.
18 As thou hast sent me into the world, even so have
I also sent them into the world.
19 And for their sakes I sanctify myself, that they
also might be sanctified through the truth.
20 Neither pray I for these alone, but for them also
which shall believe on me through their word;
21 That they all may be one; as thou, Father, art in
me, and I in thee, that they also may be one in us:
that the world may believe that thou hast sent me.

While we are positionally holy (“set free from every sin” by the blood of Christ), we know that we still sin. That’s why the Bible also refers to sanctification as a practical experience of our separation unto God. “Progressive” or “experiential” sanctification, as it is sometimes called, is the effect of obedience to the Word of God in one’s life. It is the same as growing in the Lord or spiritual maturity. God started the work of making us like Christ, and He is continuing it...

Acts 13:37-39

37 But he, whom God raised again, saw no corruption.
38 Be it known unto you therefore, men and brethren,
that through this man is preached unto you the
forgiveness of sins:
39 And by him all that believe are justified from
all things, from which ye could not be justified by
the law of Moses.

1 John 1:8-10

8 If we say that we have no sin, we deceive
ourselves, and the truth is not in us.
9 If we confess our sins, he is faithful and just
to forgive us our sins, and to cleanse us from all
unrighteousness.
10 If we say that we have not sinned, we make him a
liar, and his word is not in us.

2 Peter 3:17-18

17 Ye therefore, beloved, seeing ye know these
things before, beware lest ye also, being led away
with the error of the wicked, fall from your own
stedfastness.
18 But grow in grace, and in the knowledge of our
Lord and Saviour Jesus Christ. To him be glory both
now and for ever. Amen.

Philippians 1:9-11

9 And this I pray, that your love may abound yet
more and more in knowledge and in all judgment;
10 That ye may approve things that are excellent;
that ye may be sincere and without offence till the
day of Christ;
11 Being filled with the fruits of righteousness,
which are by Jesus Christ, unto the glory and praise
of God.

Prior to salvation, our behavior bore witness to our standing in the world in separation from God, but now our behavior should bear witness to our standing before God in separation from the world. Little by little, every day, “those who are being sanctified” are becoming more like Christ.

Reference

The Grim Reaper Preacher says, "Try reading the Bible from cover to cover - you'll like it."