6 that no one should take advantage of and defraud his brother in this matter, because the Lord is the avenger of all such, as we also forewarned you and testified.
7 For God did not call us to uncleanness, but in holiness.
8 Therefore he who rejects this does not reject man, but God, who has also given us His Holy Spirit.
take advantage (v.6) = step over, go beyond — the context here is sexual immorality
defraud (v.6) = covet, take advantage, with the idea of wanting something so much that you defraud another for your own gain — in the context, this is probably referring to coveting another person sexually to the point of taking advantage of him or her
brother (v.6) — No place else does Paul use this word of mankind in general. He always uses it of fellow believers. Some commentaries question which is meant here.
in this matter (v.6) — the context is sexual immorality — Paul’s point is probably that having sex outside of marriage is defrauding a brother of his wife (Exodus 20:17).
avenger (v.6) = one who deals justice, one who justly exacts a penalty — In Greek, frequently used of one who is a special advocate or champion of a particular city.
testified (v.6) = solemnly affirm — an intensified form of the verb translated “charged” in 1 Thessalonians 2:11.
for (v.7) — Paul is listing a second reason for possessing one’s vessel in honor — because God, who has done all for us, calls us to holiness. (The first reason is that God will exact a penalty.)
God … call[s] us in holiness (v.7) — tense indicates a definite act in the past
therefore (v.8) — indicates Paul’s concluding statement resulting from the argument has made in verses 1-7
rejects (v.8) = sets aside, disregards
has also given (v.8) — in the present tense, “gives”