This is something I'm really trying to come to grips with. As one person said, there isn't really a clear cut bible definition of whether being transgender is a sin. So we rely on whatever the leaders of our particular denomination have said for that definition. And since Christianity has, for lack of a better word, evolved with the times since Christ walked the earth, its hard to really say. I do not think that being transgender wasn't a thing in Christ's time, but I do think that because of the way the world worked in his day, it wasn't known as much, and people probably were, like we are today, afraid of what might happen if they said, 'Look, I don't really think this is how I meant to be.' Even mental illnesses were looked down upon, birth defects, all these things we are born inherently with.
I was born into a female body that so desperately tries to be male, with a mental state that I feel is more masculine than feminine. I feel for me, even if I felt my gender was female, I still am transgender, to correct all that is my body, it almost seems like a transition either way. Its hormones and other medications to make me fully function as a female, hormones and other medications, possibly surgeries to function as a male. If being transgender is a sin, then why was I born in this body with this mind? Am I supposed to just be in between?
But then, how can I be in between, if gender is critical to God's plan as my religion teaches? My religion states, 'male' and 'female' are the genders. So then, it suggests I have to pick one. But then, it seems because I was born with female parts and earned a couple more in puberty, even though they don't work, I have to pick female. But what about the male parts of me? How can I ignore those? To ignore them is almost like a death sentence.
But if I pick male, then don't I have to like women? Or is it still based on the genitals that makes the sin? But then what about the people who are born intersex? Are we to determine they are sinful just because they have physical differences from the traditional male and female?
These are just a few of the many questions I ask myself. And to be honest, I found my answer as thus: I was born this way. This is who I am. To say I am 100% female is to sin not only against myself, but also God. I cannot choose to be female anymore than I can choose to be a cat. If I choose female, I sentence my entire being to death, maybe not necessarily physically in the sense that I've gone and at the very least self-harmed, but emotionally and physically in the sense that I deny me and make my sense of self disappear. And to take something God created and to end it, that... is a sin.
All that said, it also one thing to identify as a specific gender and another to undergo reassignment surgery. I don't know if surgery truly is a sin. But my denomination, its possible to be excommunicated for it (from what I've read. I don't know all the accounts of if that's true or not). So perhaps alterations to your body may be? But I feel like, if you need to do it to live with yourself, then that's what you have to do.
That said, I am no longer an active member of my denomination, because while I do believe a majority of the tenets, I do not believe I am a sinner for my gender identity or my sexuality. And I do not like some of the policies they've come out with in regards to families of LGBT+ people.
My firm belief on the matter is, God loves us all, sinners and saints alike. And to be honest, there is no one on this earth who is a saint. No one is perfect. But I feel like those who have judged harshly will be judged harsher than those who were true to themselves, even if they were sinners because of their identity or their orientation and so on.