“But fornication and all uncleanness or covetousness,
let it not even be named among you, as is fitting for saints.”
Ephesians 5:3 

As Christians, our bodies are considered the temple of the Holy Spirit. When we have sexual intercourse with people that are not our marriage partner, we are becoming one with them and making the Holy Spirit one with them as well. Do you want to link yourself with a prostitute, worst yet, link the Holy Spirit with a prostitute?

The Apostle Paul asks us, “Do you not know that your bodies are members of Christ? Shall I then take the members of Christ and make them the members of a harlot? Certainly not! Or do you not know that he who is joined to a harlot is one body with her? For ‘the two,’ he says, ‘shall become one flesh.’ But he who is joined to the Lord is one spirit with Him. Flee sexual immorality. Every sin that a man does is outside the body, but he who commits sexual immorality sins against his own body. Or do you not know that your body is the temple of the Holy Spirit who is in you, whom you have from God, and you are not your own? For you were bought at a price; therefore glorify God in your body and in your spirit, which are God’s” (1 Corinthians 6:15-20).