What is sanctification?
Sanctification is a work of God's grace, whereby they whom God hath, before the foundation of the world, chosen to be holy, are in time, through the powerful operation of his Spirit 1 applying the death and resurrection of Christ unto them,2 renewed in their whole man after the image of God;3 having the seeds of repentance unto life, and all other saving graces, put into their hearts,4 and those graces so stirred up, increased, and strengthened,5 as that they more and more die unto sin, and rise unto newness of life.6
Scripture proofs
The Westminster Assembly's proof texts (KJV). The bracketed numbers in the answer above mark the clause each set of references supports; expand a row to read the verses.
1 Eph. 1:4; 1 Cor. 6:11; 2 Thess. 2:13
According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love:
And such were some of you: but ye are washed, but ye are sanctified, but ye are justified in the name of the Lord Jesus, and by the Spirit of our God.
But we are bound to give thanks alway to God for you, brethren beloved of the Lord, because God hath from the beginning chosen you to salvation through sanctification of the Spirit and belief of the truth:
2 Rom. 6:4–6
Rom. 6:4 Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life.
Rom. 6:5 For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection:
Rom. 6:6 Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin.
3 Eph. 4:23–24
Eph. 4:23 And be renewed in the spirit of your mind;
Eph. 4:24 And that ye put on the new man, which after God is created in righteousness and true holiness.
4 Acts 11:18; 1 John 3:9
When they heard these things, they held their peace, and glorified God, saying, Then hath God also to the Gentiles granted repentance unto life.
Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God.
5 Jude 1:20; Heb. 6:11–12; Eph. 3:16–19; Col. 1:10–11
But ye, beloved, building up yourselves on your most holy faith, praying in the Holy Ghost,
Heb. 6:11 And we desire that every one of you do shew the same diligence to the full assurance of hope unto the end:
Heb. 6:12 That ye be not slothful, but followers of them who through faith and patience inherit the promises.
Eph. 3:16 That he would grant you, according to the riches of his glory, to be strengthened with might by his Spirit in the inner man;
Eph. 3:17 That Christ may dwell in your hearts by faith; that ye, being rooted and grounded in love,
Eph. 3:18 May be able to comprehend with all saints what is the breadth, and length, and depth, and height;
Eph. 3:19 And to know the love of Christ, which passeth knowledge, that ye might be filled with all the fulness of God.
Col. 1:10 That ye might walk worthy of the Lord unto all pleasing, being fruitful in every good work, and increasing in the knowledge of God;
Col. 1:11 Strengthened with all might, according to his glorious power, unto all patience and longsuffering with joyfulness;
6 Rom. 6:4; Rom. 6:14; Gal. 5:24
Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life.
For sin shall not have dominion over you: for ye are not under the law, but under grace.
And they that are Christ’s have crucified the flesh with the affections and lusts.
This doctrine across the Standards
Where the Confession and the Westminster Shorter Catechism treat the same matter, so the question can be studied alongside its parallel statements.
In the Westminster Confession
XIII.1 They who are effectually called and regenerated, having a new heart and a new spirit created in them, …
They who are effectually called and regenerated, having a new heart and a new spirit created in them, are further sanctified, really and personally, through the virtue of Christ's death and resurrection, by his Word and Spirit dwelling in them; the dominion of the whole body of sin is destroyed, and the several lusts thereof are more and more weakened and mortified, and they more and more quickened and strengthened, in all saving graces, to the practice of true holiness, without which no man shall see the Lord.
→ XIII.1 · Of SanctificationXIII.2 This sanctification is throughout in the whole man, yet imperfect in this life; there abideth still some remnants …
This sanctification is throughout in the whole man, yet imperfect in this life; there abideth still some remnants of corruption in every part, whence ariseth a continual and irreconcilable war, the flesh lusting against the spirit, and the spirit against the flesh.
→ XIII.2 · Of SanctificationXIII.3 In which war, although the remaining corruption for a time may much prevail, yet, through the continual supply …
In which war, although the remaining corruption for a time may much prevail, yet, through the continual supply of strength from the sanctifying Spirit of Christ, the regenerate part doth overcome; and so the saints grow in grace, perfecting holiness in the fear of God.
→ XIII.3 · Of SanctificationIn the Westminster Shorter Catechism
Q.35 What is sanctification?
Sanctification is the work of God's free grace, whereby we are renewed in the whole man after the image of God, and are enabled more and more to die unto sin, and live unto righteousness.
→ Open Q.35Q.36 What are the benefits which in this life do accompany or flow from justification, adoption, and sanctification?
The benefits which in this life do accompany or flow from justification, adoption, and sanctification, are, assurance of God's love, peace of conscience, joy in the Holy Ghost, increase of grace, and perseverance therein to the end.
→ Open Q.36