To miss God’s design is to not live as God intended. It’s to sell ourselves short, to make for us lives and identities and destinies that are far, far poorer than what God intends. That’s why Christians talk about this stuff: because the good life really is possible.
Let’s begin with the observable facts of anatomy. Males have different reproductive organs than females. More than that, the reproductive organs of males appear to be designed to fit together with those of females. If you took a class on safe sex in high school, your teacher (or book, or video, or whatever) almost certainly assumed that female reproductive organs had to be treated differently than male ones. Thus, every boy in that class was expected to know how to put on a condom, and every girl in that class was expected to know what the birth control pill does. I doubt there was much confusion in the class over why girls weren’t expected to practice with condoms on themselves or the boys weren’t asking questions about the pill.
Now of course, this doesn’t prove that all the biological males in the class experienced male gender identity, or that the biological girls experienced the opposite. But the point is simply that sex education depends on a meaningful distinction between maleness and femaleness, and that this distinction is a given one, not simply an artifact of culture. No one was brainwashed into thinking they have the physical parts between their legs that they can plainly see. Boys see their boy parts, and girls see their girl parts, and from the moment boys and girls are born other people relate to them not simply as generic humans but as boys or girls, mostly because of these observable human parts.
Christianity begins with the teaching that God created a man and a woman, Adam and Eve. When Adam saw Eve for the first time, he was so excited that he broke out into song. Christians take “Bone of my bone, and flesh of my flesh” to mean that Eve was like Adam, yet unlike him. She was a human being, but she “completed” him in a very real way. In fact, in Genesis, we are told plainly how this completion was immediately expressed: through sex. “The man and his wife were both naked, and were not ashamed.” Adam and Eve’s natures as like yet unlike demanded sexual union. So in the Christian religion, men and women were created by God with bodies that are like yet unlike, and the expression of this mysterious, complementary creation is sexual union. There is no sex without bodies, and there are no bodies without maleness and femaleness.
Now here is where many critics of Christianity argue that this doctrine simply fails to describe the lived reality of many people. What about the intersex? What about those with gender dysphoria? What about those who say they know they are a different gender than their biological sex?
Two answers are in order here. First, while the existence of intersexed persons and persons with gender dysphoria is often treated like a golden gun against the Christian position, this is a gross oversimplification of what usually happens with these folks. We have research that suggests more than 90% of teens diagnosed with gender dysphoria will eventually grow out of it. Gender dysphoria should be understood as a psychological malady, not as a kind of person.
Second, the Christian position certainly anticipates the possibility of feeling alienated from one’s body. Christians believe that Adam disobeyed God and introduced sin into the world. Sin corrupted the Adam’s relationship with God, with Eve, with the earth, and even with himself. Adam and Eve’s recognition that they were naked and now ashamed is a sign of profound alienation between Adam and Eve and their bodies. Before sin, they accepted themselves and each other and rejoiced without shame. After sin, they cover their bodies and hide their persons from God.