God wants you, by your behaving in a sexually pure way, to show that you completely belong to him.

1 Thessalonians 4:3-8

3 God wants you to live pure lives that will show that you completely belong to him. He wants you to avoid doing any sexually immoral acts (OR, avoid being sexually immoral in any way). 4 That is, he wants each one of you to know how to control your own sexual desires [EUP]. He wants you to live pure lives that all people will see as good. 5 You must not lustfully desire to do immoral acts as unbelievers [MTY] do who do not obey God. 6 God wants each one of you to control your sexual desires, in order that no one of you sin against your fellow believer and take advantage of him or her by doing things like that. Remember that we strongly warned you previously [DOU] that the Lord Jesus will punish all people who do sexually immoral acts. 7 When God chose us believers, he did not want us to be people who behave in a sexually immoral way. On the contrary, he wants us to be people who behave in a morally pure way. 8 So I warn you that those who disregard this teaching of mine are not just disregarding me. On the contrary, they are disregarding God, because God commanded it. Remember that God sent his Spirit, who is holy, to live in you!