Upon acceptance of the blood of Jesus Christ for the forgiveness of sin, we become His since He bought and paid for us by His death. As His possession or servant (literally "slave"), He expressly forbids us to engage in any sexual immorality. In addition, the spirit of God's law helps us to understand fornication as unfaithfulness against one's future mate. Virginity should be held in reserve for the one we eventually marry, so he or she will not receive a mate defiled by intimacy with somebody else.
And, just as with adultery, though God forgives a fornicator of his sin, the effects of fornication will take their toll. God's law produces a penalty automatically. Sometimes it manifests itself in disease. Other times may see a child born out of wedlock or a "shotgun" marriage of two incompatible people. A few minutes of forbidden pleasure is not worth the price!
Paul writes to the Thessalonians:
For this is the will of God, your sanctification: that you should abstain from sexual immorality; that each of you should know how to possess his own vessel in sanctification and honor, not in passion of lust, like the Gentiles, who do not know God; 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. For God did not call us to uncleanness, but in holiness. (I Thessalonians 4:3-7)