The ancient Christian Church's theology about sexuality was very much influenced by Aristotle and Plato, two Greek philosophers who had very definite ideas about human beings being divided into males and females. Human beings were distinguished from the rest of creation by their ability to reason.
"For Aristotle, the male possessed a superior form of rationality, so distinctive that Aristotle ended up describing the female as a misbegotten male. Authentic human nature belonged to the procreative power of the male seed (semen); the woman provided the fertile soil for the cultivation of that seed....From the above observations, human sexuality is defined as a biological capacity for the procreation of human life. It is a biological imperative, existing solely for one purpose , namely human reproduction....And since procreation was the primary goal, any suggestion of pleasure or human fulfillment from sexual intimacy was considered an aberration.
"From a Catholic perspective it is worthy of note that marriage was not elevated to the status of a sacrament till the Council of Trent in the sixteenth century." However, Trent's understanding of marriage had not progressed. "According to Trent, marriage is defined to serve a sole purpose: the procreation of the species." (Diarmuid O'Murchu, in "Incarnation - A New Evolutionary Threshold.")
Fast-forward to the 1960's and Vatican II. Here finally, theology begins to catch up to the reality of marriage and there is a significant break-through: "In 1962...the Catholic Church changed its definition of marriage, now declared to serve a double purpose: (1) the intimacy and love of the couple for each other and (2) the procreation of the species." (O'Murchu)
But - think of the damage that had been done for generations, the guilt, shame, and repression experienced by couples who had intuitively understood the powerful force of sexual intercourse to express love and make more love, yet had had their clergy and Church and society routinely ignoring and down-playing the reality of what they were experiencing. For loving couples, physical sexual expression was bound up with the overall intimacy of their relationship, the intellectual, emotional, and spiritual connectedness between them. And only now was this being acknowledged by religion on an official level.
Also, unfortunately, because for so many generations church and society saw the male as most rational, superior to the female, a male phallic culture arose which still dominates our western society - and church.
Church and Society constructed roles "appropriate" for males and females, roles which both men and women are still seeking to break free from.
"Psychological/social stereotypes follow logically: men are supposed to be rational, assertive, tough, and focused on material success; women are supposed to be more emotional, modest, tender, and concerned with a nurturing quality of life. According to that same philosophy, the male is superior in strength, wisdom, and fertility; the woman provides the passive, receptive incubator to fertilize the male seed and assure the continuance of the human race." (O'Murchu)
We can still see these culturally conditioned stereotypes playing out in the dominant "macho" males in male-dominated action movies in which women are passive by-standers existing to fulfill male sexual fantasies, and gentle males are nerds. Or, in an understandable but not necessarily perfect reaction, women have become one-dimensional action figures in movies themselves, as capable of domination and violence as men. Yet - is this creation of a female-phallic image really a step forward in creating a more relational and compassionate society?
The Gospel stresses that human beings were created to be organically interdependent, from the womb forward, for in the womb we begin life in a relationship with our God and our mothers. We are the Body of Christ whose members are equal and need and rely on each other. Real love is expressed by emotional, intellectual, and spiritual intimacy, compassion, equality, collaboration, service, and servant leadership. The patriarchal male's "phallic" view of life (now often espoused by women as well) is characterized by the allurement of separation rather than interdependence, domination rather than cooperation, competition and hyper-individualism rather than interconnectedness, and this understanding affects all of our relationships, including our understanding of sexuality. It affects western society's understanding of "capitalism," which has become a synonym for greed, toxic competition, abuse of people and the environment, and domination.
As a western society, long repressed, we are still struggling to become truly adult in our understanding of sexuality. "Adult movies" still refer to scenes of adolescent sex games or downright sadism rather than to scenes of mature human interactions and intimacy. Magazines stress physical "positions" and activities during sex as the way to achieve the perfect orgasm rather than stressing human communication, security, commitment, and intimacy as a way to build lasting and fulfilling sexual relationships. The term "Intimacy" refers to deep connectedness at the emotional, intellectual, and spiritual level, and sometimes the sexual level as well, but males still often consider "intimacy " to refer to the sex act alone.
In our ignorance, we routinely misuse the word "eroticism." The Church's great gift to us is the spirituality and mystical tradition which developed across centuries but which was often ignored, and which rightly defines "eroticism." The word "erotic" "is extensively used (by our culture) to denote salacious, instinctual energy, widely presumed to be the basis of the lurid pornography of our time, and the promiscuous behavior that leads to so much sexual acting - out. In its original meaning, the erotic denoted the capacity for deep bonding exemplified in the life of the holy divine itself....In other words, the erotic has long been recognized as a mystical energy, through which humans seek deep intimacy with the Holy One." (O'Murchu) In other words, sexual intercourse which is tender and giving, and full of seething human desire, can give us a powerful taste of and connection to our sweetly passionate God!
Why should this surprise us? Christianity teaches us that our God is first embodied in the universe, which gives us His Presence, and then as life evolved to the level of rational humanity, God came to us embodied as a human being, Jesus, God with flesh on. If God put on a body, how can flesh in itself be evil or "less than" the soul it is united with? The Incarnation tells us that bodily sexuality is a precious gift from God.
"The body is a sacrament . . . a visible sign of invisible grace. . . . All our inner life and intimacy of soul longs to find an outer mirror. It longs for a form in which it can be seen, felt, and touched. The body is the mirror where the secret world of the soul comes to expression. The body is a sacred threshold; and it deserves to be respected, minded, and understood in its spiritual nature. . . . The body is the temple of the Holy Spirit." [See 1 Corinthians 6:19.] —John O’Donohue 
What is human sexuality then? It is more than sexual actions or procreation. Sexuality is "the totality of our creative, erotic energy, mediated through our feelings, moods, and emotions in all forms of human interaction. In a word, it is our sexuality that defines our humanity as creatures programmed with the deep desire for human relating. Our sexuality is a psychic energy that we inherit from the universe itself, fueled by the desire to relate more deeply and intimately." (O'Murchu)
Do we understand the power, glory, and joy of our God-given sexuality? Not enough. Generations of repression are still affecting marital and family relationships. Women and men pour through magazines which give suggestions about how to enhance their love-making, but they can't talk to their spouses. "Throughout much of the contemporary world, married adults often feel inhibited in speaking openly about sexual matters with their spouses or partners. Even within the intimacy of long-term monogamous relationships, human sexuality is not an easy subject for conversation. This further undermines the possibility of mature and empowering discourse with offspring, whether children or adolescents. In several Western countries, therefore, schools are expected to fill this formative vacuum, and sex education in schools rarely touches the intimate or sacred depths of what is involved in sexual flourishing and development." (O'Murchu)
Certainly, all mature adults understand the need for respectful privacy about sexuality. But if privacy descends into toxic secrecy, spouses become inhibited about discussing their respective loving and erotic needs, and also are too inhibited to pass on their sexual wisdom to their children. What takes the place of mature conversation? Pornography and addictive exploitation which pretend to be "adult" sexuality.
Currently scientists and historians are exploring gender and sex and discovering that both are more fluid concepts than society has thought and taught, and that they probably exist along a spectrum. How much more will science and history discover about human sexuality? How culturally conditioned are we as human beings? How will these findings affect our theology? No one knows.
But one step forward is Catholicism's belief that sexual orientation is not sinful in itself. Jesus treated all human beings with respect. What this practically means is that all Christians need to approach their lesbian, gay, bisexual, and transgender brothers and sisters with great love, kindness, and understanding. "Straights" need to listen to the stories of those who are different from them and recognize the scientific reality that God has created not only a planet inhabited by physically diverse species, but a sexually diverse human race. And that attentive communication with human beings who love each other and find God in their relationships with each other, whether they are "straight" or "other," expand and evolve our understanding of Who God is and how God is alive in the midst of all God's children.
Each of us as a Christian, sexed, human being has the spiritual, God-given responsibility to continue to grow in our understanding of human sexuality. Christian psychotherapist James Finley says,
"what’s at stake here, is the importance of our understanding of our God-given dignity as human beings created by God in the image and likeness of God. In God we’re created equal, and ... each person through the generosity of God is worth all that God is worth. And that value or worth isn’t based on achievement or attainment. Because parents recognize (worth) in their newborn infant. It’s that innate, inherent dignity and preciousness of the human life, which then warrants the need for it to be respected, the need for it to be protected.
"And then secondly, is that our sexuality is such a God-given, integral aspect of our human experience, our sexuality deserves to be respected as a gift. And at the very minimum it means really then that our sexual boundaries be respected, namely, that no one be sexual with us unless we want them to, that is through free consent between two adults as a free act of intimacy between two people who care about each other, want to be there for each other, as gravitating toward tenderness, closeness, warmth, fulfillment that moves toward commitment, that makes the world go around, that is the foundation of the family."