Expositor's Bible Commentary Commentary 1 Thessalonians 4:3

"For this is the will of God, [even] your sanctification, that ye abstain from fornication;" — 1 Thessalonians 4:3 (ASV)

Christian holiness requires total abstinence from “sexual immorality” (GK 4518). This word requires a broad definition as including all types of sexual sins between male and female. A year or two earlier a Christian council in Jerusalem had ruled decisively on a related issue affecting Gentile Christians (cf. Acts 15:20). It is not clear whether the Thessalonians were guilty of such immorality, so common among the pagans (v.5). Though Paul may have had in mind the temptation to indulge in it, his strong words probably imply some overt transgressions. Pagan moral corruption looked upon fornication either indifferently or favorably. That the Thessalonians slipped into it after their conversion would not have been strange. While Paul had congratulated them on their faith (cf. 1:3), this does not mean that there was no occasional misbehavior, even this kind, within the church (cf. 1 Corinthians 1:4–9; 5:1–5; 6:12–20).