Looking through the history of the Lords interaction with humanity he has only selected male priests. From Melchizedek to Aaron to the apostles.  

He certainly never commanded a female priesthood at any time, like he never commanded man to become pregnant or women to deliver sperm. The fact is that priesthood is connected to fatherhood. A man cannot be a mother no matter how much we desire total equality, just like no woman can be a father. 

Why did God setup two sexes if there was not meant to be a difference? 

Countless pagan faiths have priestesses, it would have been the easiest thing in the world to do as the Montanists an conform to pagan practice.