1 Thessalonians 4:3

3 It is God’s will that you should be sanctified: that you should avoid sexual immorality;

Read 1 Thessalonians 4:3 Using Other Translations

For this is the will of God, even your sanctification, that ye should abstain from fornication:
For this is the will of God, your sanctification:that you abstain from sexual immorality;
God’s will is for you to be holy, so stay away from all sexual sin.