Ambrose of Milan — On the Mysteries, ch. 9, §50

“Perhaps you will say, "I see something else, how is it that you assert that I receive the Body of Christ?" And this is the point which remains for us to prove. And what evidence shall we make use of? Let us prove that this is not what nature made, but what the blessing consecrated, and the power of blessing is greater than that of nature, because by blessing nature itself is changed.”