Every generation presents rival ideas to the truths of Scripture, and the truth of Scripture must be clarified and re-clarified against the rival ideas in each age. The superficial understanding that was sufficient in a prior age will no longer do. Preaching needs to speak to the rival ideas of the present age, informed by a deeper understanding of things that were always revealed in Scripture but not always stated in Scriptural bold print.
We live in an age where the church is beset from both outside and from inside, with powerful, rival ideas about gender and sexuality. These rival ideas of gender and sexuality are part of an even broader set of beliefs. As these ideas enter the church, they are challenging our ability to trust the What that is written in Scripture by sowing doubt into the Why. I believe the Why of sex and gender boundaries is revealed in Scripture, even if it is not always stated in the same bold print as the What.
Laying the foundation for the Why requires taking a closer, deeper look at the revelation of Creation. The revelation of creation as articulated in Romans 1 is based on this premise: everything that God has made was designed to impress his character upon us, and we were designed to be impressed upon by what has made to comprehend the qualities of the invisible God. When the Psalms 19 talks of the heavens declaring the glory of God, this is only to highlight one aspect of creation fulfilling this role in our lives, not by any means to exclude all the rest of Creation from doing so.
Our own making as part of the Revelation of Creation is special in two keys ways: 1) our making was specifically made in God’s Image unlike any other thing that was made, and 2) we experience our making from the inside-out, whereas we experience everything else in creation from the outside-in. If the heavens, being far away and not specifically made in God's image, have things to teach us about God, how more so does our own making, which was specifically made in God's image and that we experience from the inside out?
Sexuality is the domain where we experience our making in a uniquely powerful way, where our differences between male and female and are intended to impress upon us special aspects of the character of God. Sexuality is where we experience those aspects of God's character which are more uniquely and completely represent in women compared to men, and in men compared to women. Though the act of sex is part of sexuality, it is not necessary to be in a sexual relationship for us to experience the instructive power our sexuality to reflect God's image and impress upon us aspects of God's character.
God, being above sexuality, is not made in sexuality’s image, though human sexuality is made to reflect certain aspects of God’s image. Pagan religions, like the ancient Egyptians, saw sexuality as a fundamental aspect of reality, of fertility, death and rebirth that was represented in both the gods and in human flesh, and so they conceived of their god’s as being made in the image of sexuality.
Sexuality is a quality of human creation that functions to reflect God’s image, though God himself, being divine, is above sexuality. In the similar manner, if I were to make a clay statue in the image of the person, I would need to do certain things to the clay (like sculpting it and baking it) that are not appropriate for the person. The clay would then have a limited, specific way that it would convey information about the person it was representing. So it is, in a roughly similar fashion, that sexuality is a quality of human existence that God has created for a special purpose to reflect certain aspects of God’s character, but it is not something that directly correlates to a quality of God.
The boundaries on sexuality, encompassing sexual and gender behavior in Scripture are put there so that the revelation of Creation expressed through the sexual aspect of our making functions as it was intended to properly reflect and illumine the nature of God and how we relate to him as his children. The power of sexuality is such that it is either powerfully involved in reflecting God's image for our benefit or it is powerfully diverting us into sexual idolatry.
Sexual immorality is the result of sexual idolatry caused by sexual confusion, where sexual energy is not operating in it's God-ordained way.