“…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“
In verse six, Paul makes another appeal for sexual purity – the impact sexual sin has on your illicit sexual partner.
that no one should take advantage of
The words “should take advantage” denote to go over, used metaphorically as “transgress.” The context refers to “passion of lust” so the topic is sexual sins. Someone who takes “advantage of” someone else steps over God’s boundaries.
The New Testament uses this term in the commercial sense as well. Violating someone else’s wife is like stealing from them.
Adultery is like stealing.
Many people’s activities fly in the face of God’s boundaries or prescribed limits. Sexual sins transgress God’s standards in dealing with fellow Christians.
This is no different that stealing someone’s property. We have no more right to have sex with someone’s spouse because they are attractive to us any more than we have a right to steal their car because it appeals to us.