The Apostle Peter informs us that each Person of the Holy Trinity has a distinct work in the salvation of God’s people:

Elect according to the foreknowledge of God the Father, through sanctification of the Spirit, unto obedience and sprinkling of the blood of Jesus Christ.
 1 Petrus 1:2

The distinct work of the Father is to choose those sinners who are to be saved; the work of the Son is to cleanse us by His blood; the work of the Spirit is to sanctify those so elected by the Father and so cleansed from their sin by the Son.

We need to be clear as to the differences between Sanctification and Justification:

1. Justification alters our legal standing before God as our Judge; Sanctification is a process by which the justified sinner is made progressively holy.
    
2. In Justification God imputes to us the righteousness of Christ; in Sanctification God works upon our fallen nature to make it increasingly holy.
    
3. So, Justification is an ACT of God, which is done at once, as soon as He pronounces us ‘Not guilty’, when we believe in Jesus Christ for salvation; Sanctification is a lifelong WORK of God and is not complete till the believer enters the state of death.

Because in Sanctification God is working to put our whole soul right we must, as His people, expect to go through difficult and humbling experiences. Sin is deeply ingrained in our whole nature and so, if we are to be a holy people, we must expect to have to go through many trials and struggles in this process of becoming holy. Sanctification is, according to Samuel Rutherford, the ‘stormy north side of Christ’. ‘Our pride’, he says, ‘needs winter weather to rot it’. Sanctification was the great emphasis of the Puritans, just as Justification had been that of Luther and the Reformers.

The Puritans of the Westminster Assembly defined Sanctification in this way:

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. 
Shorter Catechism A. 35

Several things need to be noticed in this fine definition:

1. Sanctification is a life-long process.
    
2. It is a progressive work, in which the believer grows in holiness.
    
3. Each particular Christian is at a different stage of this process, so that some are more advanced in holiness than others.

In the light of the fact that God loves holiness and commands us to be holy, it is one of the great duties of the believer to cooperate with God’s Spirit in this process of becoming sanctified.

In the New Birth we do not cooperate, but are entirely passive, since the New Birth is a creative act of God. By this act the whole soul is renewed in the image of God. From hating God, as previously we did, we now love God and desire to please Him. All five faculties of the soul now become active in the believer: mind, will-power, affections, conscience and memory.

The instinct of a newly-born person is to wish to live in fellowship with God, to enjoy God’s love and to aim at God’s glory. This we are to do by our style of life and by our habits, words and total behaviour. The justified and converted sinner is now a ‘new creature’ in Christ.

Therefore, in this process of Sanctification, we are called on to co-operate with God: ‘work out your own salvation with fear and trembling’ (Phil. 2:12). A powerful motive is given to us to do so: ‘For it is God which worketh in you’ (Phil. 2:13). Rabbi Duncan well defined for us the nature of Sanctification: ‘It is all the work of God, and all the work of man’. We must work at it.

Mistakes are made by some when they try to understand this subject. One mistake is to suppose that a Christian may become perfect in this life. This is an error. The problem the believer has is that there is an opposing force in his soul which frustrates his desire for perfection. We refer to this opposing force of the soul as ‘indwelling sin’. It is in every one of the five faculties.

The very best Christian is in this life imperfect in Sanctification. Sadly, we see that King David could make a grievous mistake even at a mature stage of life. Peter too could deny his Lord whom he truly loved. And Paul had to confess:

The good that I would I do not; but the evil that I would not, that I do
Romans 7:19

This honest assessment of our progress in personal holiness must be that of every believer so long as he is in this life. Complete moral and spiritual perfection, however, is given to the Christian in the instant of death. In the moment of physical death the true believer will be perfectly and eternally sanctified and so fitted for life in glory.

To make progress in Sanctification is absolutely impossible before the New Birth. This was the classic mistake of the Pharisees of Christ’s day. They foolishly imagined that they could live a holy life by strictly conforming to man­made rules. But Christ exposed their error repeatedly: ‘A good tree bringeth not forth corrupt fruit; neither doth a corrupt tree bring forth good fruit’ (Luke 6:43). We cannot make ourselves holy; but after God has made us holy at our New Birth we must seek to advance in godliness.

Sadly, this same mistake is made by monks and nuns and other devout persons, who endeavour after holiness while as yet they have not been converted by the re-creative act of God, which we call the New Birth.

A further mistake concerning Sanctification is made by some evangelical Christians who believe that God lowers the standard of holiness for His people after conversion. The name we give to this is New Covenant Theology. The mistake is the failure to see that God requires nothing short of perfection from all mankind, whether believers or not. Since God is absolutely just and holy He cannot require of us anything less than absolute moral perfection.

To make this clear to believers, Jesus has stated:

Think not that I am come to destroy the law ... Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law...
Matthew 5:17-18

God requires of all mankind absolute and total conformity to His Moral Law, summed up in the Ten Commandments. The unbeliever cannot keep God’s commandments and, unless he repents and believes in Christ, he will suffer eternal punishment for his disobedience. The true Christian cannot perfectly keep God’s commandments, but because he is justified by the imputation to him of Christ’s righteousness he will be forgiven his sins.

The temptation for the Christian is to suppose that God requires less of him than a total obedience to the Moral Law, the Ten Commandments. But this is the error which Christ corrects in the above reference to Matthew 5:17­-18.

There is only one standard laid down by God for Christian and non-Christian: ‘Be ye therefore perfect, even as your Father which is in heaven is perfect’ (Mt. 5:48). Again the Word of God declares: ‘For whosoever shall keep the whole law, and yet offend in one point, he is guilty of all’ (James 2:10). It is our duty as Christians to aim for nothing less than perfection in all we do, say or think. We must not excuse our shortcomings but rather bemoan them, as Paul does: ‘O wretched man that I am! Who shall deliver me from the body of this death?’ (Rom. 7:24). BB Warfield defines the true biblical attitude of the believer in these words: ‘The Reformers represented the Christian life as a life of continuous dissatisfaction with self, and of continuous looking afresh to Christ as the ground of all our hope’. We are sorry to be so far from perfect; but we rejoice that Jesus our Saviour is perfect — and will in the end make us perfect too. This is the balanced attitude to holiness we are to take in this life. It reminds us that sin is still sin, even in the very best of believers. A time will never come when we shall not need the blessed Lord Christ as our perfect righteousness.

How then are we to look at God’s dealings with the believer when he, or she, sins? God will never punish the Christian; but He may well chasten him for sin. Punishment is judicial; chastisement is fatherly discipline. If we wish to avoid chastisement we must take seriously the call to mortify sin and to strive after perfection.

The mistake at the root of New Covenant teaching is to suppose that the Ten Commandments are the ‘old covenant made with Israel at Sinai and with no other’. The doctrine we are to hold to is this: ‘The Christian is not under the Ten Commandments as a Covenant but as a Rule of Life’. The justification for this doctrine is to be found clearly in Romans 7, where Paul explains that at our New Birth we are divorced from the Moral Law as a Covenant but are, nevertheless, bound in conscience to adopt the Ten Commandments as our Christian Rule of Life. We are not, as believers, obliged to keep the Ten Commandments in order to obtain salvation; but we are, as those who are saved, obliged to keep these Commandments out of love and gratitude to God, whose Law they are. So Christ tells us: ‘If ye love me, keep my commandments’ (John 14:15).

In short, then, our task as Christians is to work hard to govern our thoughts, words and deeds so that they conform to God’s law: to love God above all, and our neighbour as ourself. The immature believer may at first think this an easy task. But as he matures he will realise, as he did not previously, that his whole way of life is deeply influenced by his own depravity, concupiscence, pride and unbelief. As he matures he learns to trust himself less and, now painfully aware of his inconsistencies, to cry out to God for help.

The Apostle Peter and Judas Iscariot both sinned. But there is a world of difference between them. Peter sinned as a born-again and a justified man. Judas sinned as a godless hypocrite. Both lamented over their own actions. But Peter’s sin was pardoned for Christ’s sake, whereas Judas’ sin, being that of an unjustified man, is still being punished in hell — and will be to all eternity.

Because the believer is in union with Christ the Holy Spirit gives him enabling grace. ‘Sin shall not have dominion’ over him’ (Rom. 6:14). Even so, the believer’s duty is to give diligence to grow in every virtue and in every good habit of life. Two things which the Christian must learn to do are to put to death all bad actions, and to practise all that is good. The terms for this are Mortification (putting to death) and Vivification (stirring into life). The simple illustration is that of the good gardener. He must do these two things: FEED and WEED. So must we as God’s people.

Vitally important to Sanctification are these good habits: regular secret prayer, Bible study and meditation, reading good Christian books, fellowship with other believers, self-examination, and a diligent use of the Sabbath Day. Our generation very much needs to see good examples of godly believers who take the duties of Sanctification seriously. All believers are equally justified, but they are not all equally sanctified. God will bless the careful Christian, who will get his reward either in this life, or in the next — or in BOTH.