I'm not in anyway versed in the Bible but I assume is a sin to be trans. Each individual is divine as in it has a soul but we are also responsible for our actions. Even if the kid has gender dysphoria, the kid and father should try to deal with his/her mental illness rather then give in to it.

His argument can be made about anything, sociopath, gay, pedophiles etc. Just because they have a soul and God loves them does not mean He approves of their choices and actions.