Why are some issues directly followed such as the OT's ban on homosexuality while other things such as using birth control is allowed(which is anti literial biblical) and stoning is not allowed?
Of course it is all predetermined anyways......
The Bible is consistent on the subject of Homosexuality in both the old and the new testament.
A good number of Reformed Christians agree that birth control ought not to be used but I am not sure that an ironclad case can b e made from Scripture against it.
Stoning is just a way of executing people.
Behind all this though I think we have the issue of what the nature of the Law is for the Church.
A rule of thumb is that if it is repeated and underlined in the New Testament (Murder, Homsexuality, Adultery, Fornication are sinful) then it is clearly binding on the church.
A further distinction is made between moral, civil and ceremonial Law.
Moral Law is unchanging, we can see that because nearly every instance of moral prescription is uniform throughout Scripture.
Not so with ceremonial and civil Law. We no longer sacrifice animals and we no longer apply civil penalties for transgression of the Mosaic Law (though some Reformed folks would like to say that we should). In each case an argument can be made for the abrogation of these aspects of the Mosaic legislation, this abrogation being either total (as in the case of ceremonial prescriptions) or endlessly argued about and ultimately evaluated on a case by case basis when it comes to civil requirements.
There are differing opinions, my own is that liberty should be the guiding principle, we have been set free by Christ from the penalty of the Law. The moral law is still binding only in the sense that it pictures that law "written on our hearts" (Rom. 2:15) that Paul speaks of.
In any case, there is now no condemnation for us (Rom. 8:1)