Translators of the Revised Standard Version have put the heading “Exhortation to purity” above our text. This is correct. The apostle Paul stresses in this Scripture passage that the Lord calls his children to lead a holy life. Faith and life are inseparable. Whoever wants to follow Christ, will also have to lead a different life. Believers may never forget that they have been redeemed with the precious blood of Christ from their empty way of life (cf. 1 Pet 1:18).

Paul speaks in his letters quite often about this sanctification of life. Checking   this closely we discover that Paul never speaks in a legalistic manner about the sanctification of God’s children.  He always exhorts us from the gospel. The work of God in Christ is always first and foremost.

Everything Paul says about our sanctification has the Old Testament as background. God already called Israel to holiness. We find a principal word in the book of Leviticus in chapter 19:2: “Be holy because I, the LORD your God, am holy.” The word used in the Hebrew Old Testament for “holy” is derived from the root qad, which literally means “separate.” Someone who is holy is therefore “separated” or “set apart.”  At first this sounds very negative but that is not how it is meant in the Old Testament.  The point is: to be separated from something in order to be fully focused on something else.

Israel has been separated from all other nations, in order to be God’s own people, his treasured possession (cf. Deut 7:6). By grace Israel may belong to the LORD as a kingdom of priests and a holy nation (cf. Ex 19:6).

Because the LORD has so sanctified Israel for him self, therefore they must now also live in holiness, completely dedicated to him. Also for the Old Testament it is true that the call to a holy life sounds forth out of the gospel of God’s mighty deeds. It says repeatedly that it is the LORD who sanctifies Israel (cf. Lev 20:8; 21:8; 22:32). This is beautifully expressed in Leviticus 20:26: “You are to be holy to me because I, the LORD, am holy, and have set you apart from the nations to be my own.” Israel may live out of God’s sanctifying grace.

The call to sanctification is nothing else but an exhortation to give full passage to this grace of God.

When the apostle Paul speaks about sanctification, he very clearly continues this line even further. Nowhere does he teach that sanctification is something man must bring about. The congregation has been given the sanctification of life in Christ. Christ is also our sanctification (cf. 1 Cor 1:30). He gave him self up for his congregation, to sanctify her, to make her holy (cf. Eph 5:26).

When the apostle speaks in 1 Thessalonians 4 about sanctification, he does so from the perspective of the salvation that has been granted to the church in Christ. Paul asks and exhorts in the Lord Jesus (cf. v. 1). This means he addresses them on the basis of the grace given to them in the Lord Jesus. Out of this grace they have to live. This grace has to completely control and govern all they do.

For it is God’s will that his children should be sanctified (cf. v. 3). This applied already in the old covenant. It is also valid in the new covenant. The life of the congregation has to answer to the grace that has appeared for her in Christ.

There is a reason why Paul speaks so emphatically about sanctification in chapter 4. The recent converts in Thessalonica had a hard time to pull themselves away from the pagan lifestyle of their city. Especially with regard to marriage and sexuality there was much lacking in a holy, Christian lifestyle. Paul warns emphatically against sexual immorality. In marriage or while engaged to be married, the Thessalonians should not be controlled by passionate lust but by holiness and honor (cf. v. 4). Anyone who sexually lives it up, without a care about God’s commandment, brings God’s judgment on himself. The Lord is an Avenger of all this. His holiness does not tolerate such unholiness!

Paul draws a final conclusion in our text. Whoever rejects his serious warnings to a holy walk of life, does not reject a man but God. Behind Paul as the apostle stands the Lord. In all that Paul points out to them, they are confronted with the call of God him self.

The apostle especially accentuates his final warning by reminding the Thessalonians that God has given them his Holy Spirit. Paul uses the present tense: God gives his Holy Spirit. He reminds his readers that the Spirit works in the congregation and that she is his temple. The Spirit is continually at work in the congregation. He wrestles to impart to her what she has in Christ. The apostle’s emphasis becomes even stronger when we translate: “who, after all, even gives you his Holy Spirit.” Also in the area of sexuality and marriage we have to be holy and honorable, for God gives his Holy Spirit, the Spirit whose task it is exactly, to sanctify the congregation (cf. 2 Thess 2:13), to present her as a pure bride without stain or blemish (cf. Eph 5:27).

Paul does not mention the work of the Holy Spirit in so many words in our text. But from the whole context it is evident that the apostle thinks here of the sanctifying work of the Spirit. The Spirit does a great many things. All his work in and for the congregation can be summed up in the word “sanctification.”  The work of the Spirit is aiming at the continuing increasing “separation” of the congregation and her dedication to the Lord Jesus. It is completely correct when the Heidelberg Catechism, in Lord’s Day 8, brings sanctification to the fore as the specific work of the Holy Spirit.

Whoever continues to live in passionate lust, denies the wonderful and glorious work of God’s Holy Spirit.

All across the board, Christians have to lead a life different from those who do not know God; also during engagement and in marriage. For Christ sanctifies his congregation by his Holy Spirit. The work of this Spirit reaches out to the great day on which the congregation is presented to her Bridegroom, as a pure Bride, radiant, without stain or wrinkle (cf. Eph 5:27).

What Paul writes in our text is a serious warning but at the same time a great encouragement. The struggle to live in holiness, especially during engagement and in marriage, can be heavy. Throughout Scripture we read how sexuality is a door through which the evil one attacks us by his powerful temptations. Children of God stumble so easily, especially in this area.

Paul comforts us. We do not stand alone in this struggle! God gives us his Holy Spirit. Divine powers are at work in us to make us strong whenever we are weak, to keep us standing every time we are in danger of falling.

God desires our sanctification. But to our comfort we may know that this sanctification is his gift. It is the Holy Spirit who sanctifies and renews us and who does not rest till he has finally presented us without blemish among the assembly of God’s elect in life eternal.

The first principle of a holy walk of life, also in sexuality and marriage, is: to let the Lord work in us through his Spirit, and make way for the great Gift which Christ obtained for his people.