One reason we don't make a greater impact on the world is that too many people who profess faith in Jesus and attend church regularly lie without blinking an eye, cheat on their taxes, pull dishonest business deals, break their marriage vows, hold bitter grudges, spread malicious gossip, and despise the downtrodden in society while overlooking the evils of the rich and successful. Paul was writing to us as well as to the believers in Thessalonica when he interspersed practical Christian-life admonitions throughout these letters. Pagan society in the first century was marked by sexual permissiveness. So believers needed to be reminded that God wants His people to be distinctive by their chastity. Christians are to keep their passions under control because their bodies belong to God.
Adultery always defrauds someone other than the two participants in the act.
The unmarried who commit fornication wrong their future partner by not being able to bring into their marriage the virginity one has a right to expect. God will punish sexual impurity because it violates the whole character of the Christian life and is outright disobedience to the One who has given us the Holy Spirit to enable us. Paul said that the Holy Spirit had taught his readers to love one another, that they were doing it, and that they should continue to do so. We know that the love God demands means being kind, forgiving, helpful, and tender toward others regardless of how we feel toward them. We must therefore choose to be loving.