Nietzsche's Error

I think the error that people like Nietzsche make is in thinking that Christianity is an a posteriori code of rules that one has to adopt. It isn't. It is an a priori doctoring of the soul that better fits its treated patients to go back out into the posteriori world and engage. There are no prescriptions for behaviour in the a posteriori world just the assumption that healthy souls will wish of themselves to be decent, brave, kind-hearted etc because those are the qualities of a normal nature unhampered by sin.