This phrase "one flesh" is used only seven times in the Bible: four times in the three verses just cited, as well as Matthew 19:5; Ephesians 5:31; and I Corinthians 6:16. This final scripture elevates the "one flesh" principle, revealing a spiritual correspondence:
Do you not know that your bodies are members of Christ? Shall I then take the members of Christ and make them 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. (I Corinthians 6:15-17)
How sacrilegious it would be to try to force Christ into a union with a harlot! Yet, that is what members of the church do when they give themselves over to un-Christian behavior, since they have been joined to Christ by covenant. He is the Bridegroom, and the church is the Bride. Such iniquity, Paul suggests, is the spiritual counterpart to a married man having sexual relations with a woman who is not his wife.
As shown previously, coitus—whether inside or outside of marriage—binds a man and woman as one flesh. Joined in verse 16 is derived from the Greek word kolláō, which means exactly the same thing as the Hebrew word dabaq in Genesis 2:24: "to glue together," "to cleave," "to adhere." Paul is plainly stating that, as the conjugal relations of a couple bind them together like glue, so also does the illicit act of a man and a harlot unite them as one flesh.
In the Old Testament, writers often used forms of the verb "to know" as a euphemism for the sexual act (see Genesis 4:1; I Samuel 1:19; etc.). This "knowing" suggests that the actual intercourse is but the physical sign of the greater personal and emotional intimacy that is shared—even with a prostitute. "Uncovering the nakedness" of another, as is written throughout Leviticus 18, is such an intimate act that it creates a bond between the two participants.
Too many people of this generation think of sex as cheap. Since the publication of the Kinsey Report in the late 1940s and the early 1950s, the doors of promiscuity have been flung wide open, spawning the sexual revolution. Nowadays, it raises few eyebrows that some have multiple sexual partners, even before graduating from high school! While Americans of all beliefs shake their heads in consternation over Tiger Woods' string of illicit liaisons, the truth is that this kind of scandalous behavior is quite commonplace in Main-Street America.
God does not consider the sexual union of man and wife as cheap. As the author of Hebrews writes, "Marriage is honorable among all, and the bed undefiled; but fornicators and adulterers God will judge" (Hebrews 13:4). To Him, it is so valuable that every time a person engages in it, he more intimately binds himself to his spouse, making marriage even more precious. Clearly, the "one flesh" principle is vital to Christian marriage.
However, the sexual aspect of this principle should not distract us because, in fact, the focus is on the closeness of union or togetherness. Without using the term "one flesh" again, the apostle expands on how this principle applies to marriage in I Corinthians 6:18-20; 7:2-4. He writes, "You are not your own" (I Corinthians 6:19), and "You do not have authority over your body, but your spouse does" (I Corinthians 7:4, paraphrased).
This is a major Christian understanding, one that separates it from marriages in other religions. Once married—once joined as a unit—the individuals in the covenant (husband and wife, male and female) are subsumed within the bond. To use a sports analogy, the team becomes more important than the individual players. The principle of "one flesh" leads to absolute togetherness or unity—living, thinking, planning, working as one.
This is obviously the ideal. It should not embarrass anyone or make anyone feel like a failure if this kind of total oneness is not present in his or her own marriage. It may never happen. Even so, God expects married couples to work toward the goal of being so committed to the relationship, so much in love with each other, so willing to work harmoniously together, that they function as a perfectly oiled unit, as it were.
We should never forget that marriage is a type of something greater! What does God want of us? To be one spirit with Him (I Corinthians 6:17)! The marriage relationship, where a man and a woman come together as one flesh, is a training program for the majority of us to learn how to be one with Him. If we cannot be one flesh with the person closest to us, how can we hope to be of one spirit with God?
Marriage is a primary spiritual testing-ground for us to prepare to be the Bride of Jesus Christ our Savior and to be one with God. Thus, we learn how to work in tandem with another human being whom God has given to us as a mate. Like a yoke of oxen, we must learn to pull in the same direction and for the same purposes, straining to reach the same ultimate glory.
How are we married couples doing? Are we pulling together? Or have we agreed to something like a 50/50 marriage? God would frown upon a 50/50 marriage because what it implies is that one is willing to meet his spouse only halfway. God desires us to give everything up to the other—so much that we no longer even own ourselves! Each spouse owns the other. That is surrendering a great deal, but it is also receiving much in return.
In Song of Songs 6:3, the Shulamite, after experiencing the trauma of being beaten and abused by wicked men in her town, comes to realize that the "one flesh" principle is the way a marriage should work. She says: "I am my beloved's, and my beloved is mine." She understands that her spouse has done everything for her benefit, and because she was his and he was hers, she would do everything for him.
This is as good as it gets, humanly speaking. The perfect marriage is one in which each partner is wholly committed to the other and to the relationship. Each mate is striving to the utmost to live according to the will of God by showing true love—outgoing concern—for the other. And the perfect mate is the loving Christian giving his all to develop God's character both in himself and in his spouse.