Sanctification is God’s gracious work by which those united to Jesus Christ are really and personally renewed after God’s image, increasingly freed from the power of sin, and enabled to live in holiness.
Paul writes:
“For this is the will of God, even your sanctification.” — 1 Thessalonians 4:3
Sanctification belongs to every true Christian.
God does not merely change the believer’s legal standing through justification and then leave his character untouched. The same Christ who provides righteousness for His people also gives His Spirit to transform them.
Yet sanctification must be distinguished carefully from justification.
Justification is God’s once-for-all judicial act declaring the believer righteous because of Christ’s imputed righteousness.
Sanctification is God’s continuing work of grace renewing the believer himself.
We are justified by a righteousness outside us.
We are sanctified as God works holiness within us.
Both come from union with Christ, and God never separates them.
What Is Sanctification?
The Larger Catechism describes sanctification as a work of God’s grace in which the Holy Ghost applies the death and resurrection of Christ to those God chose to be holy, renews them throughout the whole person after God’s image, implants saving graces, and increasingly enables them to die to sin and rise to newness of life (WLC 75).
That definition contains several important truths.
Sanctification is God’s work.
Sanctification produces real change.
Sanctification concerns the whole person.
Sanctification is rooted in Christ.
Sanctification involves both putting sin to death and growing in righteousness.
And sanctification progresses throughout the Christian life.
We should add one further qualification: sanctification does not begin merely as an almost imperceptible lifelong improvement.
At conversion, something decisive has already happened.
Sanctification Begins with a Decisive Break from Sin’s Dominion
WCF 13.1 says that in those who are effectually called and regenerated, “the dominion of the whole body of sin is destroyed.”
That statement matters.
A Christian may still battle powerful temptations and may sometimes fall grievously, but sin no longer occupies the throne it once held.
Paul asks:
“How shall we, that are dead to sin, live any longer therein?” — Romans 6:2
He later declares:
“Sin shall not have dominion over you.” — Romans 6:14
This does not mean that the Christian has become sinless.
It means that the ruling relationship has changed.
Before regeneration, sin reigns.
After regeneration, remaining sin fights.
Those are not the same condition.
Sanctification therefore includes both a definitive beginning and a progressive outworking.
The kingdom of sin has been broken, but many enemies remain within its former territory.
The Christian life is the long work of putting them to death.
Sanctification Flows from Union with Christ
The power of sanctification does not arise from human determination detached from Christ.
WCF 13 says believers are sanctified “through the virtue of Christ’s death and resurrection.”
Romans 6 explains why.
Those united to Christ are united to the Christ who died and rose. His death means a decisive breach with the dominion of sin; His resurrection introduces them into newness of life.
Paul writes:
“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.” — Romans 6:4
Sanctification is therefore gospel-shaped.
The Christian does not merely look at Jesus as an external moral example and attempt to copy Him through determination.
Christ’s Spirit dwells within His people.
His death and resurrection exert saving power upon them.
We pursue holiness because we belong to the crucified and risen Christ.
Sanctification Renews the Whole Person
Sin affects the whole person, and sanctification reaches the whole person.
WCF 13.2 says sanctification is “throughout, in the whole man.”
God renews the mind so that we increasingly think according to truth.
He reforms desires so that what once seemed attractive begins to appear hateful.
He trains the affections so that we increasingly love what God loves.
He redirects the will toward obedience.
Even the body comes increasingly under the service of righteousness.
Paul therefore urges:
“Neither yield ye your members as instruments of unrighteousness unto sin: but yield yourselves unto God.” — Romans 6:13
Sanctification cannot be reduced to visible behavioral modification.
Someone may outwardly avoid a sin because reputation, fear, pride, or convenience restrains him while the heart continues to cherish it.
Biblical holiness reaches desires, motives, imagination, thoughts, words, relationships, and conduct.
God is restoring His image in the whole person.
Mortification: Putting Sin to Death
One side of sanctification is traditionally called mortification.
Paul writes:
“If ye through the Spirit do mortify the deeds of the body, ye shall live.” — Romans 8:13
To mortify is to put to death.
Christians are not called merely to manage sinful habits so that they cause less inconvenience. We seek the death of sin.
That requires more than suppressing outward behavior.
We learn to identify sinful desires at their roots, confess them honestly, refuse occasions that feed them, bring the Word of God against their lies, and actively deny them obedience.
Yet Romans 8:13 contains an indispensable phrase: “through the Spirit.”
Mortification is strenuous Christian activity carried out in dependence upon divine power.
We do the putting to death.
The Spirit supplies the power by which it is done.
Any approach that removes either truth becomes distorted. Passive spirituality waits for holiness without effort. Legalistic self-reformation attempts holiness without dependence upon grace.
Biblical sanctification requires active faith working by the Spirit.
Vivification: Growing in New Obedience
Sanctification involves more than saying no to sin.
The old Reformed term vivification describes the corresponding growth of new spiritual life.
Paul speaks of believers being “alive unto God through Jesus Christ our Lord” (Romans 6:11).
The thief stops stealing and begins honest labor and generosity.
Corrupt speech is replaced with words that minister grace.
Bitterness gives way to forgiveness.
Pride is opposed by humility.
Sexual impurity is displaced by chastity.
Self-centeredness gives way to love of God and neighbor.
Sanctification therefore removes weeds and cultivates fruit.
The Spirit produces “love, joy, peace, longsuffering, gentleness, goodness, faith, meekness, temperance” (Galatians 5:22–23).
Holiness is more than becoming less visibly sinful.
It is becoming increasingly fruitful in righteousness.
Sanctification Is Progressive
Unlike justification, sanctification is incomplete in this life.
WCF 13.2 says remnants of corruption remain in every part of the believer.
Paul describes the conflict:
“For the flesh lusteth against the Spirit, and the Spirit against the flesh.” — Galatians 5:17
This explains a common Christian experience.
Conversion does not make temptation disappear.
Indeed, new spiritual life often makes us more conscious of sins we once barely noticed.
Growth in holiness can therefore coexist with a growing awareness of our remaining corruption.
A mature Christian may sometimes feel more sinful than he did years earlier, not because sanctification has failed, but because greater light reveals stains that darkness concealed.
Progress should therefore be measured carefully.
Real sanctification produces genuine change, but growth is rarely a smooth upward line.
There are seasons of rapid advance, seasons of painful struggle, and seasons in which remaining corruption appears frighteningly strong.
Can a True Christian Fall Seriously into Sin?
Yes.
Westminster is realistic.
WCF 13.3 acknowledges that remaining corruption may “for a time, much prevail.” WCF 17.3 goes further and says true believers may fall into grievous sins through temptation, remaining corruption, and neglect of the means of grace.
David did.
Peter did.
The existence of a serious fall therefore does not prove automatically that regeneration never occurred.
But neither should this truth be used to trivialize sin.
Serious sin brings God’s fatherly displeasure, wounds conscience, weakens assurance, grieves the Spirit, harms others, and may bring severe temporal consequences.
The promise is that sin will not recover final dominion over the true believer.
Through the continual supply of the Spirit, grace ultimately prevails.
The Christian may lose battles.
Christ will not lose the war for His child.
Is Christian Perfection Possible in This Life?
No.
Scripture gives no support to the claim that Christians may reach a state in this life in which all inward sin has been eradicated.
John writes:
“If we say that we have no sin, we deceive ourselves, and the truth is not in us.” — 1 John 1:8
Paul, though mature in Christ, says:
“Not as though I had already attained, either were already perfect.” — Philippians 3:12
WCF 13.2 therefore says sanctification remains imperfect in this life.
This should not make us complacent.
The same Paul who denied having attained perfection pressed toward the mark.
The impossibility of sinless perfection before glory does not excuse tolerated sin. It explains why the Christian life remains a warfare until the end.
We never graduate from repentance.
If We Are Justified by Faith Alone, Why Is Holiness Necessary?
Because the Christ who justifies also sanctifies.
Hebrews commands:
“Follow peace with all men, and holiness, without which no man shall see the Lord.” — Hebrews 12:14
This does not mean holiness earns the right to see God.
Christ alone merits salvation.
Sanctification is necessary in another sense: it is an inseparable part and fruit of God’s saving work.
A person who claims justification while remaining permanently content beneath the dominion of sin misunderstands grace.
Saving faith receives a whole Christ.
Christ pardons.
Christ gives righteousness.
Christ also gives His Spirit and breaks the power of sin.
Good works are therefore necessary as fruits and evidences of genuine faith, as acts of gratitude and obedience, and as part of the holy life for which God saves His people.
They are never the basis upon which God justifies us.
The order must remain clear.
We pursue holiness because we have been accepted in Christ, never in order to construct a righteousness that will persuade God to accept us.
What Role Does God’s Law Have in Sanctification?
Grace does not make God’s moral law irrelevant.
WCF 19.6 teaches that although believers are no longer under the law as a covenant of works by which they must earn life, the law remains a valuable rule of life.
It shows us God’s will.
It exposes remaining sin.
It teaches us what love and holiness look like in practice.
It drives us repeatedly to Christ by exposing how far short we still fall.
The Spirit and the law therefore are not enemies.
The Holy Ghost who sanctifies us is the same Spirit who inspired the commandments.
Christian obedience is neither an attempt to earn justification nor an exercise in inventing our own definition of holiness.
We learn holiness from God’s Word.
How Does God Sanctify His People?
God ordinarily sanctifies through the means He has appointed.
Jesus prayed:
“Sanctify them through thy truth: thy word is truth.” — John 17:17
The Word of God is therefore central.
The Spirit uses Scripture read, preached, remembered, believed, and obeyed to renew the mind and expose sin.
God also strengthens His people through the sacraments, prayer, the fellowship and discipline of the church, and the ordinary providences through which He tests faith and develops endurance.
These means can appear unspectacular.
Christians sometimes seek dramatic experiences that will suddenly remove lifelong struggles, while neglecting the ordinary channels God has promised to use.
Sanctification is normally cultivated through repeated exposure to the Word, prayer, Lord’s Day worship, the sacraments, Christian fellowship, repentance, and ordinary obedience.
God makes saints by means of grace.
What Is the Christian’s Role in Sanctification?
Because sanctification is God’s work, some have imagined that strenuous effort reveals a lack of faith.
Paul reasons differently:
“Work out your own salvation with fear and trembling. For it is God which worketh in you both to will and to do of his good pleasure.” — Philippians 2:12–13
God’s work becomes the basis for ours.
The Christian watches and prays.
He flees temptation.
He disciplines his thoughts.
He confesses sin.
He makes restitution where necessary.
He puts harmful patterns away.
He pursues obedience even when he does not feel inclined toward it.
He makes use of the Word and prayer.
All of this is genuine human activity.
Yet beneath it stands the prior and continuing work of grace.
We labor because God works in us.
Sanctification and Assurance
Growth in holiness can strengthen assurance because the fruits of grace provide evidence of God’s work.
Yet Christians must handle this carefully.
If we make our sanctification the foundation of assurance, our peace will become as unstable as our performance.
The primary ground of assurance remains God’s promises in Christ.
The fruits of sanctification serve as confirming evidence.
A believer should therefore be concerned if there is no warfare against sin, no repentance, and no desire for holiness.
But he should not demand perfect holiness before daring to believe that Christ receives him.
Even weak grace is grace.
The question is not whether we have arrived.
It is whether spiritual life is present and whether Christ remains the object of our faith.
Sanctification Will Be Completed
The conflict with sin does not continue forever.
At death, the souls of believers are made perfect in holiness and enter the presence of God. At the resurrection, their bodies will be raised in glory, and redemption will embrace the whole person.
John writes:
“We know that, when he shall appear, we shall be like him; for we shall see him as he is.” — 1 John 3:2
What sanctification begins, glory completes.
No Christian will carry a beloved sin into the new creation.
No temptation will survive resurrection.
No disordered affection will remain.
No believer will forever mourn the gap between what he ought to be and what he is.
God chose His people “that we should be holy” (Ephesians 1:4).
Christ gave Himself to purify a people for His own possession.
The Spirit now renews them after God’s image.
And the work will succeed.
The final hope of sanctification is not that Christians will eventually become sufficiently disciplined to perfect themselves.
It is that the Savior who began His work will bring His people, body and soul, into unblemished holiness before His presence.
Until then, grace teaches us to fight.
Westminster references: WCF 13.1–3; 14.1–3; 16.1–6; 17.1–3; 19.6–7; WLC 69, 75–78; WSC 32, 35–36, 88–90.