Saint Augustine 
On Nature and Grace 

At that time also there came into my hands a certain book of Pelagius’, in which he defends, with all the argumentative skill he could muster, the nature of man, in opposition to the grace of God whereby the unrighteous is justified and we become Christians. The treatise which contains my reply to him, and in which I defend grace, not indeed as in opposition to nature, but as that which liberates and controls nature, I have entitled
On Nature and Grace.