Good question and one that comes up in various forms frequently.
The first part to the question is often along the lines of “If God is all-knowing, why didn’t He deal with orientation in the Scriptures though those who authored the books?” That response is here. Along similar questioning, “Why was the topic of sexual orientation not discussed or investigated until recently?” That response is here.
The final part of your question merits its own response. Of course, my response is speculation since the Bible does not answer a question that could not have even been asked before the last century at the earliest and realistically, not even until the most recent 50 years.
Many of us who are affirming have been able to apply the same views of intimate relationship enjoyed by those who are heterosexual to those who are somewhere else along the spectrum of human sexuality. We know, actually all of us should realize, that the Bible was written in the context and framework of extreme patriarchy and gender hierarchy. The language, the social and sexual roles would have been deeply reflective and in alignment with those structures.
Bible authors could not write or even hear from a context they would have never known or imagined. Approval of healthy, loving, monogamous, sacrificial same-sex relationships were unheard of until the mid 20th century. This is strictly tied to the role of women in cultures. As patriarchy and gender hierarchy were challenged, woman escaped the subjugation of men. Yet, we KNOW the Bible has been used to hold women in submission for millennia. (Patriarchy has been in place culturally for over 12,000 years since the dawn of the agricultural revolution for humans. That is a LOT of entrenched structure to overcome!)
We also know the Bible has been used to subjugate slaves and people of color in particular. Some may want to dismiss this as an embarrassment, but history and records tell the story. A great read on this subject is The Civil War as a Theological Crisis by Mark Noll. Another good theological read on the use of the Bible to subjugate both people of color and women is Ancient Laws and Contemporary Controversies by Dr. Cheryl Anderson.
Slowly by slowly, those from outside the white, heterosexual, male dominant class are looking to the Scriptures and interpreting them through a more inclusive lens. There is no doubt that the lens in which the original language is written and then has been interpreted is white, heterosexual, and male. My goodness, surely others are included in Jesus’ inclusive Kingdom!
And here we are again. LGBT people have been consistently and actively knocking on the church doors since the beginning of gay activism in the 1960s asking for the church to PLEASE listen to them. I cover this well in Chapter 13 of my book Walking the Bridgeless Canyon entitled The Beginning of the Gay and Trans Christian Movement.
We’ve been here before. Biblical support of slavery was challenged. The subjugation of woman was/is being challenged. And now, those who are not in amongst the heteronormative are challenging the interpretive lenses. Great!
When those lenses are challenged and the gender restrictive barriers are lifted from passages, we CAN see God’s blessing of same-sex unions. I wrote a whole series on same-sex marriage that should answer most questions along this line. Lots of information is packed in these posts.
The last part of my response is a personal views. I have now moved freely in and out of the affirming and non-affirming church environments for about 15 years. I know thousands of LGBT Christians. The finest examples I know of Christlike behavior are embodied within the LGBT community. They know grace, mercy and forgiveness overall far better than we in the non-affirming church do. They have MUCH to show and teach us.
Not only have a experienced an incredible growth in my own Christian witness and faith while doing this justice work, I have seen the same exponential growth in other allies and advocates who are joined in this movement for justice.
The church needs not only the gifts of LGBT Christians, we need the experience of learning what grace actually means. Stretching ourselves beyond our understanding and “like list” forces us to be better instruments and recipients of grace — and after all, is that not the basic foundation of Christianity?
For whatever is God’s reason, now is the time we are called to struggle with this new expansion of who is in and who is out according to God, not according to man. We are equipped with resources, the witness of LGBT Christians and the gift of relationships and learning from others. The church will become inclusive. We are called to be a people who pray the Kingdom in on earth. The Kingdom is inclusive (Gal. 3:28).
I have been able to align my faith and beliefs about human sexuality and gender identity fully with the Scriptures. I have made an effort to understand context and challenged the man-made lenses of the Bible to find the inclusive heart of God.