God designed both maleness and femaleness, and God designed us individually as males and females.
God authored gender.
He didn’t do it because someone forced His hand (no one can). He didn’t do it as a response to sin (when He started maleness and femaleness there was no human sin). He did it out if His own beautiful, perfect, creative, glorious will.
“The Lord God took the man and put him in the garden of Eden to work it and keep it… Then the Lord God said, “It is not good that the man should be alone; I will make him a helper fit for him.’ Now out of the ground the Lord God had formed every beast of the field and every bird of the heavens and brought them to the man to see what he would call them. And whatever the man called every living creature, that was its name. The man gave names to all livestock and to the birds of the heavens and to every beast of the field. But for Adam there was not found a helper fit for him. So the Lord God caused a deep sleep to fall upon the man, and while he slept took one of his ribs and closed up its place with flesh. And the rib that the Lord God had taken from the man he made into a woman and brought her to the man. Then the man said,
‘This at last is bone of my bones and flesh of my flesh; she shall be called Woman, because she was taken out of Man.’ Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh.”
From this we know at least one thing clearly: God made man and told him to tend His garden, and since it was not good for him to do it alone He made woman to be his helper.
The New Testament repeats this: “For man was not made from woman, but woman from man. Neither was man created for woman, but woman for man,” (1 Corinthians 11:8-9).
The reason that you don’t see God inviting men to marry men or have romance with them, or saying that gender is a flexible thing you can choose is not that God was just playing to an ancient audience that was sadly behind the times.
Christ was never afraid to speak unpopular truth to people who loved their cultures more than His Word. If you read Matthew, Mark, Luke, and John, you’ll find a Jesus who cares far more about people’s souls than their feelings. Who cares far more about what’s true than what’s trendy.
No, the reason you don’t see those things in the Bible is that the Bible assumes and states that God authored gender, that He defines it, and that He assigns it. He made Adam Adam, and He made Eve Eve. And it was good and beautiful and a reflection of His character and His awesomeness. It reflects Him and draws attention to Him (especially when redeemed and made clean by Christ).
Again from the New Testament: “Wives, submit to your own husbands, as to the Lord. For the husband is the head of the wife even as Christ is the head of the church, his body, and is himself its Savior. Now as the church submits to Christ, so also wives should submit in everything to their husbands.
Husbands, love your wives, as Christ loved the church and gave himself up for her, that he might sanctify her, having cleansed her by the washing of water with the word, so that he might present the church to himself in splendor, without spot or wrinkle or any such thing, that she might be holy and without blemish. In the same way husbands should love their wives as their own bodies. He who loves his wife loves himself. For no one ever hated his own flesh, but nourishes and cherishes it, just as Christ does the church, because we are members of his body. ‘Therefore a man shall leave his father and mother and hold fast to his wife, and the two shall become one flesh.’ This mystery is profound, and I am saying that it refers to Christ and the church. However, let each one of you love his wife as himself, and let the wife see that she respects her husband.”
God breathed, created, spoke man. And from Adam He created woman. The God who designed light and and space and sound waves made male and female in His image.
He created one for one thing and one for another. One to tend a garden and the other to help him. One gender primarily to give himself for his wife and love her and wash her by the Word, and the other gender primarily to submit to her husband (though both also do in ways submit to each other) and be cleaned and, like 1 Peter 3 says, be gentle.
Yes, God made each person to be different. Some, he says, are like an eye. Others like an ear. Others like a hand.
But He also made each of us either a male or a female. And when we rebel against what He made those to be, we rebel against Him.
Against a good Father who knows what’s best. And against a Lord who has all authority to create.