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First Thessalonians, part 8, Christian Morality

In chapter 4, Paul moves from recounting his relationship with the Thessalonians to giving more direct instruction about sanctification. The transition follows naturally from his prayer at the end of chapter 3: “so that He may establish your hearts without blame in holiness before our God and Father...”

Paul now explains what that holiness looks like in practical terms. In verses 1–6 his principal concern is sexual morality, but he frames the whole discussion in terms of walking in a manner pleasing to God.

1 Thessalonians 4:1 begins,

¹ Finally then, brethren, we request and exhort you in the Lord Jesus, that as you received from us instruction as to how you ought to walk and please God (just as you actually do walk), that you excel still more.

The word “walk” (peripateō) is a common biblical metaphor for one’s manner of life. The Hebrew Scriptures use the same imagery. God’s commandments define the path in which His people are to walk. For example, see Deuteronomy 5:32,

³² So you shall observe to do just as the LORD your God has commanded you; you shall not turn aside to the right or to the left.

Paul therefore does not separate faith from conduct. Conversion changes the believer’s walk. Yet Paul is careful to acknowledge that the Thessalonians were already doing this: “just as you actually do walk.” His exhortation is therefore not a rebuke so much as a call to “excel still more.”

The Greek perisseuō means to abound, overflow, or increase beyond measure. The same idea appeared earlier in 1 Thessalonians 3:12, “may the Lord cause you to increase and abound in love.” Christian maturity is progressive. One may genuinely please God and yet still have much room to grow.

Kingdom Culture Based on God’s Law

1 Thessalonians 4:2 continues,

² For you know what commandments we gave you by the authority of the Lord Jesus.

The word translated “commandments” is parangelia, meaning an instruction, charge, or authoritative command. Commandments are laws. Paul stresses that these were not merely his personal opinions. It is “by the authority of the Lord Jesus.” In other words, the Lord Jesus did not put away the laws or commandments (Matthew 5:17), even though some forms of the law were altered on account of the New Covenant (Hebrews 7:12).

This is important because Paul will shortly give instructions concerning sexual conduct. He is not merely imposing Jewish cultural customs upon Gentile believers. The law of God is an expression of God’s very nature, and this provides a universal standard of morality. Jewish cultural customs derive from men’s understanding of the law—the traditions or doctrines of men—and are only as valid as their conformity to actual biblical truth.

Paul views these moral requirements as expressions of the authority of Christ. This also agrees with Jesus’ Great Commission in Matthew 28:20: “teaching them to observe all that I commanded you.”

The leading of the Holy Spirit, therefore, does not abolish obedience. The Spirit writes the law on the heart so that God’s commands may be fulfilled from within, that is, by nature, rather than by external compulsion. That is the provision of the New Covenant (Jeremiah 31:33).

Paul then makes an unusually explicit statement concerning God's will in 1 Thessalonians 4:3,

³ For this is the will of God, your sanctification; that is, that you abstain from sexual immorality.

The Greek word for “sanctification” is hagiasmos, from the same family of words as hagios, “holy.” Sanctification means being setapart for God. It is about being different and acting under a higher moral standard that the world considers to be good. Paul does not leave holiness as an abstract theological concept. He immediately applies it to sexual conduct: “that you abstain from sexual immorality.”

The word translated “sexual immorality” is porneia. It is a broad term encompassing all unlawful sexual relations, whether it be adultery, homosexual relations, or sexual relations outside of a lawful marriage. This instruction would have been especially significant in Thessalonica. The converts were living in the Greco-Roman world, where many forms of sexual conduct forbidden by biblical law were culturally tolerated.

The Greek expression, Κορινθία κόρη (Korinthia korē), literally “Corinthian girl” or “Corinthian maiden,” in ancient Greek usage, was a common euphemism for a prostitute or courtesan.

There was even a Greek verb: κορινθιάζομαι (korinthiazomai) — “to act like a Corinthian,” commonly understood as to practice sexual immorality or live promiscuously. Keep on mind that Paul was writing his letter from Corinth. Believers in Christ were expected to give evidence of their faith by repentance—a change of heart, a new mindset, a new standard of morality.

A famous Greek proverb was: “Not for every man is the voyage to Corinth.” In other words, not all men indulge in prostitution. Paul would have agreed. Christian believers do not take that voyage to immorality.

The Jerusalem Council had already singled out sexual immorality as something Gentile converts were specifically required to abandon in Acts 15:29, “that you abstain from things sacrificed to idols and from blood and from things strangled and from fornication [porneia].”

This prohibition did not originate with Paul. It rested ultimately upon God’s definition of lawful and unlawful sexual relations.

Leviticus 18 gives the most extensive biblical list of prohibited sexual relationships. Significantly, that chapter applies the moral standard not merely to Israelites but also to the nations that occupied Canaan before them. God says their sexual sins had defiled the land (Leviticus 18:24–28). Those who teach that the law was given only to Israel and that other nations were not judged by its standard of measure do not understand the mind of God.

Thus, porneia cannot simply be defined by whatever a particular culture considers acceptable. God’s law supplies the standard and establishes the definition of sin (1 John 3:4).

1 Thessalonians 4:4, 5 says,

⁴ that each of you know how to possess his own vessel in sanctification and honor, ⁵ not in lustful passion, like the Gentiles who do not know God.

The expression “possess his own vessel” has generated considerable discussion. The Greek reads: to heautou skeuos ktasthai, literally, something like “to acquire/possess his own vessel.”

There are two major interpretations. One understands the “vessel” as one’s own body. This has biblical parallels. Paul calls human beings “earthen vessels” in 2 Corinthians 4:7, and Peter refers to the wife as a “weaker vessel” in 1 Peter 3:7. On this interpretation Paul means: Learn to control your own body in holiness and honor.

The second interpretation understands “vessel” as being satisfied and loyal to one’s wife, so that Paul is speaking of acquiring or living with a wife honorably rather than satisfying sexual desire through immorality. There is some support for this usage in Jewish thought, and the verb ktaomai can mean to acquire rather than merely to control. In other words, acquire a wife, not a prostitute.

Either way, Paul’s central point is clear: sexual desire must be governed by holiness and honor rather than by lust. He contrasts this with “the Gentiles who do not know God,” people who follow standards of behavior that differ from the law of God.

Lustful Passion vs the Holy Spirit

Paul’s point is not that sexual desire itself is sinful. God created sexuality. The issue is whether desire is governed by God’s order or whether desire becomes the governing principle. Paul calls the latter “lustful passion.” The Greek is pathos epithymias, literally something like “passion of desire.” The believer is not to be ruled or governed by the soul’s fleshly appetite.

This principle extends far beyond sexuality. The difference between spiritual maturity and carnality is often revealed by the question: Who is master—the person under God, or his appetites? Incidentally, many Greek philosophers repeatedly asked essentially the same question: Does reason govern the passions, or do the passions govern the man?

The similarity in vocabulary and concept would have made Paul’s teaching readily understandable to a Greek audience, though Paul’s theological foundation was quite different.

Plato gives perhaps the most influential formulation. In the Republic, Plato divides the soul into three aspects: reason (logistikon), spirit (thymos), and appetite/desire (epithymētikon). The healthy person is one in whom reason rules and the other elements occupy their proper place. Disorder occurs when appetite takes control.

This becomes particularly vivid in Plato’s description of the tyrannical man in Republic Book IX. Political tyranny has its counterpart within the individual: a man may appear free while actually being enslaved to his desires. Thus Plato develops a paradox that later moralists frequently repeated: The man who does whatever his appetites demand is not truly free; he is their slave.

This comes very close conceptually to Paul's statement in Romans 6:16:

¹⁶ Do you not know that when you present yourselves to someone as slaves for obedience, you are slaves of the one whom you obey...?

Aristotle distinguishes between knowing what is good and actually possessing sufficient character to act accordingly. He speaks of akrasia — lack of self-control, incontinence, literally a condition of not having mastery. Its opposite is enkrateia — self-control or mastery.

This Greek vocabulary is especially interesting for New Testament study because enkrateia becomes a Christian virtue. Paul lists it as a fruit of the Spirit in Galatians 5:23,

²³ gentleness, self-control [enkrateia]; against such things there is no law.

Yet Paul differs fundamentally from the philosophers. Plato, along with the Stoics and other philosophers, essentially said Reason must rule appetite. Paul says in Galatians 5:16,

¹⁶ But I say, walk by the Spirit, and you will not carry out the desire [epithymia] of the flesh.

The solution is the rule of the Holy Spirit within the believer—not mere human reasoning, which, though good, is constantly undermined by faulty premises.

Transgressing and Defrauding

In 1 Thessalonians 4:6, Paul adds an important dimension that is sometimes overlooked:

⁶ and that no man transgress and defraud his brother in the matter because the Lord is the avenger in all these things, just as we also told you before and solemnly warned you.

Sexual immorality is not merely a private act between consenting individuals. It may involve an offense against a third party. The words are strong. “Transgress,” translated from hyperbainō, literally means to step beyond or overstep a boundary. “Defraud,” translated from pleonekteō, means to take advantage of another, exploit him, or gain something at his expense.

This gives Paul’s discussion a distinctly legal character. Adultery, for example, does not merely violate an abstract moral rule. It violates a marriage covenant and wrongs another person. One has crossed a God-established boundary and taken what rightfully belongs within another covenant relationship. This is consistent with the law prohibiting adultery (Exodus 20:14).

The final part of verse 6 is particularly significant, “because the Lord is the avenger in all these things.” The Greek word is ekdikos, one who executes justice or punishment. This recalls the law in Deuteronomy 32:35, “Vengeance is Mine, and retribution.”

Paul quotes this same principle explicitly in Romans 12:19: “Vengeance is Mine, I will repay.” Therefore, when Paul says that “the Lord is the avenger,” he is invoking the principle of divine justice. The injured party is not authorized to pursue personal vengeance. Judgment belongs to God, who judges according to righteousness.

This also explains why Paul says, “just as we also told you before and solemnly warned you.” Apparently sexual morality was part of Paul’s basic gospel instruction to new converts. Even though his stay in Thessalonica had been relatively short, he had already taught them that God’s grace did not eliminate moral accountability or the law itself.

Paul does not define holiness merely in ceremonial or mystical terms. Holiness is the practical application of divine law through a heart governed by the Spirit. This is particularly evident in verse 6. Sexual sin is not merely “unclean;” it is an act that can transgress and defraud another person. Hence it becomes a matter of justice as well as personal morality.

This sets up verse 7 very naturally:

⁷ For God has not called us for the purpose of impurity, but in sanctification.

The calling of God is therefore a calling not merely from sin, but into holiness—a way of life in which our desires are brought into agreement with God's order and our relationships with others are governed by love rather than covetousness.