Paul calls the Thessalonians to keep growing in a life that pleases God by pursuing sanctification in sexual holiness. They must abstain from sexual immorality, practice honorable self-control, and refuse conduct that wrongs others, because this is God’s will and calling. To reject this instruction is not to reject man, but God.

Paul begins a new section of exhortation, yet it is closely connected to what came before. In 3:13 he prayed that they would be established in holiness, and here he urges them to live that holiness out more and more. He appeals to them "in the Lord Jesus," showing that this instruction comes with the Lord’s authority, not merely Paul’s personal opinion.

He reminds them that they had already received teaching about how they ought to live in order to please God, and he gladly recognizes that they are already walking in that way. Paul is not writing as if they have completely failed. He encourages them, while also pressing them forward. Christian obedience is not something static; it is meant to increase.

He also says they already know the commands he gave them through the Lord Jesus. These moral demands were part of their basic Christian instruction from the beginning. Sexual holiness was not treated as an optional subject or an advanced matter for a few mature believers. It belonged to ordinary discipleship.

Then Paul states the matter plainly: "This is God’s will: your sanctification." Here, God’s will does not refer to hidden guidance about personal decisions. It refers to God’s revealed moral will. In this passage, that will is expressed concretely in a life of holiness, especially in sexual conduct.

So Paul says they must abstain from sexual immorality. The word porneia is broad and refers to illicit sexual conduct, not just one narrow offense. God’s will for his people includes real separation from sexual sin.

In verse 4, Paul says that each believer must know how to possess his own body in holiness and honor. This wording is genuinely debated. Some understand it to mean acquiring a wife in an honorable way, and that remains possible. Still, in this context, the stronger view is that Paul is speaking about learning to exercise control over one’s own body. The contrast with lustful passion fits that understanding best. In either case, the main point is clear: sexual conduct must be governed by holiness and honor, not by lust.

Paul then says this must be "not in lustful passion like the Gentiles who do not know God." This is not a license for ethnic pride or contempt. The contrast is theological and moral. Paul is distinguishing those who know the true God from pagan life marked by ignorance of God. In his argument, sexual conduct is closely tied to the knowledge of God.

Verse 6 shows that sexual sin is not merely a private matter of impurity. It can also wrong another person. When Paul says that no one should violate or take advantage of his brother "in this matter," the most natural reading is that he is still speaking about sexual sin, not suddenly shifting to business fraud. The point likely includes sexually exploitative conduct, such as adultery and related sins, without requiring us to define every possible case too precisely.

Paul adds a solemn warning: "the Lord is the avenger in all these cases." This is judicial language. The Lord sees such wrongs and will deal with them justly. Paul says he had already told them this and warned them seriously, so this was not a new emphasis but part of his earlier apostolic instruction.

In verse 7, Paul grounds the command in God’s call: God did not call believers for impurity, but in holiness. God’s saving call has a moral purpose. He calls his people to a life marked by holiness.

Paul then sharpens the conclusion: whoever rejects this instruction is not rejecting man, but God. To dismiss apostolic teaching on sexual holiness is to refuse God’s authority.

He adds that this is the God who gives his Holy Spirit to them. God’s ongoing gift of the Spirit makes rejection of this teaching even more serious. These commands come from the holy God who is actively at work among his people.

Taken together, these verses show that sexual holiness is part of living in a way that pleases God. It belongs to sanctification, reflects the knowledge of God, protects others from wrong, and stands under the Lord’s judgment. This paragraph does not say everything Paul teaches elsewhere about marriage or sexuality, but what it does say is clear: believers must reject sexual immorality and live in holiness and honor, because this is God’s will and God’s call.