God wants people to live holy lives (Leviticus 11:44a; Leviticus 19:2). That is a life in which his commandments are final. Therefore a Christian should refrain from fornication. The Greek word here (πορνεία) means that sexual intercourse outside the marriage relationship is contraband. This is what was also decided at the council in Jerusalem (Acts 15:20; see also Acts 21:25). Since then this rule counted for every gentile who became a Christian. In the Greek world of that time with its sexual morality, the Christians obviously stood out. Thus it certainly took courage to be a Christian.
3 For this is the will of God, your sanctification: that you abstain from sexual immorality;