By Robert A. J. Gagnon, Special to CNN

Editor’s Note: Robert A. J. Gagnon, Ph.D., is associate professor of New Testament at Pittsburgh Theological Seminary and author of The Bible and Homosexual Practice: Texts and Hermeneutics and (with Dan Via) Homosexuality and the Bible: Two Views.

In her recent CNN Belief Blog post “The Bible’s surprisingly mixed messages on sexuality,” Jennifer Wright Knust claims that Christians can’t appeal to the Bible to justify opposition to homosexual practice because the Bible provides no clear witness on the subject and is too flawed to serve as a moral guide.

As a scholar who has written books and articles on the Bible and homosexual practice, I can say that the reality is the opposite of her claim. It’s shocking that in her editorial and even her book, "Unprotected Texts," Knust ignores a mountain of evidence against her positions.

It raises a serious question: does the Left read significant works that disagree with pro-gay interpretations of Scripture and choose to simply ignore them?

Owing to space limitations I will focus on her two key arguments: the ideal of gender-neutral humanity and slavery arguments.

Knust's lead argument is that sexual differentiation in Genesis, Jesus and Paul is nothing more than an "afterthought" because "God's original intention for humanity was androgyny."

It’s true that Genesis presents the first human (Hebrew adam, from adamah, ground: “earthling”) as originally sexually undifferentiated. But what Knust misses is that once something is “taken from” the human to form a woman, the human, now differentiated as a man, finds his sexual other half in that missing element, a woman.

That’s why Genesis speaks of the woman as a “counterpart” or “complement,” using a Hebrew expression neged, which means both “corresponding to” and “opposite.” She is similar as regards humanity but different in terms of gender. If sexual relations are to be had, they are to be had with a sexual counterpart or complement.

Knust cites the apostle Paul’s remark about “no ‘male and female’” in Galatians. Yet Paul applies this dictum to establishing the equal worth of men and women before God, not to eliminating a male-female prerequisite for sex.

Applied to sexual relations, the phrase means “no sex,” not “acceptance of homosexual practice,” as is evident both from the consensus of the earliest interpreters of this phrase and from Jesus' own sayings about marriage in this age and the next.

All the earliest interpreters agreed that "no 'male and female,'" applied to sexual relations, meant "no sex."

That included Paul and the ascetic believers at Corinth in the mid-first century; and the church fathers and gnostics of the second to fourth centuries. Where they disagreed is over whether to postpone mandatory celibacy until the resurrection (the orthodox view) or to begin insisting on it now (the heretical view).

Jesus’ view

According to Jesus, “when (people) rise from the dead, they neither marry nor are given in marriage but are like the angels” (Mark 12:25). Sexual relations and differentiation had only penultimate significance. The unmediated access to God that resurrection bodies bring would make sex look dull by comparison.

At the same time Jesus regarded the male-female paradigm as essential if sexual relations were to be had in this present age.

In rejecting a revolving door of divorce-and-remarriage and, implicitly, polygamy Jesus cited Genesis: “From the beginning of creation, ‘male and female he made them.’ ‘For this reason a man …will be joined to his woman and the two shall become one flesh’” (Mark 10:2-12; Matthew 19:3-12).

Jesus’ point was that God’s limiting of persons in a sexual union to two is evident in his creation of two (and only two) primary sexes: male and female, man and woman. The union of male and female completes the sexual spectrum, rendering a third partner both unnecessary and undesirable.

The sectarian Jewish group known as the Essenes similarly rejected polygamy on the grounds that God made us “male and female,” two sexual complements designed for a union consisting only of two.

Knust insinuates that Jesus wouldn’t have opposed homosexual relationships. Yet Jesus’ interpretation of Genesis demonstrates that he regarded a male-female prerequisite for marriage as the foundation on which other sexual standards could be predicated, including monogamy. Obviously the foundation is more important than anything predicated on it.

Jesus developed a principle of interpretation that Knust ignores: God’s “from the beginning” creation of “male and female” trumps some sexual behaviors permitted in the Old Testament. So there’s nothing unorthodox about recognizing change in Scripture’s sexual ethics. But note the direction of the change: toward less sexual license and greater conformity to the logic of the male-female requirement in Genesis. Knust is traveling in the opposite direction.

Knust’s slavery analogy and avoidance of closer analogies

Knust argues that an appeal to the Bible for opposing homosexual practice is as morally unjustifiable as pre-Civil War appeals to the Bible for supporting slavery. The analogy is a bad one.

The best analogy will be the comparison that shares the most points of substantive correspondence with the item being compared. How much does the Bible’s treatment of slavery resemble its treatment of homosexual practice? Very little.

Scripture shows no vested interest in preserving the institution of slavery but it does show a strong vested interest from Genesis to Revelation in preserving a male-female prerequisite. Unlike its treatment of the institution of slavery, Scripture treats a male-female prerequisite for sex as a pre-Fall structure.

The Bible accommodates to social systems where sometimes the only alternative to starvation is enslavement. But it clearly shows a critical edge by specifying mandatory release dates and the right of kinship buyback; requiring that Israelites not be treated as slaves; and reminding Israelites that God had redeemed them from slavery in Egypt.

Paul urged enslaved believers to use an opportunity for freedom to maximize service to God and encouraged a Christian master (Philemon) to free his slave (Onesimus).

How can changing up on the Bible’s male-female prerequisite for sex be analogous to the church’s revision of the slavery issue if the Bible encourages critique of slavery but discourages critique of a male-female paradigm for sex?

Much closer analogies to the Bible’s rejection of homosexual practice are the Bible’s rejection of incest and the New Testament’s rejection of polyamory (polygamy).

Homosexual practice, incest, and polyamory are all (1) forms of sexual behavior (2) able to be conducted as adult-committed relationships but (3) strongly proscribed because (4) they violate creation structures or natural law.

Like same-sex intercourse, incest is sex between persons too much structurally alike, here as regards kinship rather than gender. Polyamory is a violation of the foundational “twoness” of the sexes.

The fact that Knust chooses a distant analogue (slavery) over more proximate analogues (incest, polyamory) shows that her analogical reasoning is driven more by ideological biases than by fair use of analogies.

Knust’s other arguments are riddled with holes.

In claiming that David and Jonathan had a homosexual relationship she confuses kinship affection with erotic love. Her claim that “from the perspective of the New Testament” the Sodom story was about “the near rape of angels, not sex between men” makes an "either-or" out of Jude 7’s "both-and."

Her canard that only a few Bible texts reject homosexual practice overlooks other relevant texts and the fact that infrequent mention is often a sign of significance. It is disturbing to read what passes nowadays for expert “liberal” reflections on what the Bible says about homosexual practice.

The opinions expressed in this commentary are solely those of Robert A. J. Gagnon.