“Fidelity: What it means to be a one-woman man” was printed in 1999. Doug Wilson comments on 1 Corinthians 6:15-17:
“Know ye not that your bodies are the members of Christ? shall I then take the members of Christ, and make [them] the members of an harlot? God forbid. What? know ye not that he which is joined to an harlot is one body? for two, saith he, shall be one flesh. But he that is joined unto the Lord is one spirit. (vv. 15-17)
In other words, because the believing man is united with Christ, is one with Him, if he then engages in behavior which also makes him one with a whore, he has involved Christ in his sin. Sexual activity always results in a one-flesh union. The passage quoted by Paul is from Genesis and was originally speaking of marriage, and it is quoted elsewhere by him and is applied to marriage (Eph. 5:31). But a one flesh union occurs whether or not a marriage has been contracted. There is no incongruity between the holy covenantal union with Christ on the one hand and holy sex within the bounds of holy matrimony on the other. There is a fundamental incongruity between this holiness in Christ and cavorting with a hooker” (Douglas Wilson, Fidelity, p. 43).
Wilson correctly acknowledges that sexual activity ALWAYS results in a one-flesh union. And what IS this one-flesh union ALWAYS referred to as? Everywhere and always in Scripture, a one-flesh union is referred to as MARRIAGE — sometimes lawful and sometimes unlawful, but always a marriage. The one who cavorts with the hooker, becomes one-flesh with the hooker (see 1 Corinthians 6:16; Genesis 2:24). Wilson writes:
“But a one flesh union occurs whether or not a marriage has been contracted.”
A marriage is always necessarily and inevitably contracted as a result of every one-flesh union. So the question is NOT WHETHER a marriage was contracted as a result of sex, BUT WHAT kind of marriage was contracted? Was a wicked and adulterous marriage contracted, or was a non-adulterous, God-honoring, and God-pleasing marriage contracted? Is this one-flesh union a dishonoring and defiling of the marriage bed (cf. Hebrews 13:4)? A one-flesh union ALWAYS results in a marriage — not necessarily a lawful marriage of course, but an actual marriage nonetheless.