“Overstep...his brother” refers to adultery with the brother's wife. In Greek “take advantage of” also means make a gain of; hence, defraud. By “the matter” Paul means the matter of fornication, mentioned in verse 3. In verse 6 Paul also says that the Lord is the avenger concerning these things, things such as overstepping and taking advantage of others. The Lord judges the fornicators and adulterers as an avenger, as a punisher, meting out justice. Fornication always involves overstepping the regulation of the marriage relationship. The relationship between male and female was ordained by God. Marriage is a holy matter that was ordained by God and is under His strict regulation. Therefore, the contact between male and female must be according to God's ordination and regulation. Otherwise there may be some kind of transgression, overstepping, breaking of God's regulation. The apostle's charge to abstain from fornication is based upon sanctification (v. 3), strengthened by sanctification (v. 4), and concluded here [in v. 7] with sanctification, because fornication, as the most unclean thing, destroys the holy standing and character of God's called saints.

Bible verses are taken from the Recovery Version of the Bible and Words of Ministry, from Witness Lee, Life- study of Thessalonians, pp.133-134. Both are published by Living Stream Ministry, Anaheim.