St Ambrose on Corpus Christi

St Ambrose, who may well be the first to refer to the Eucharistic Mystery as the ‘Mass’, has left us two great works that deal with the Eucharist: Of Sacraments and Of Mysteries, both of them published around 300ad. The following selections are taken from Of Mysteries.
Image and reality

Now consider which is more excellent, the bread of angels [i.e. the manna] or the Flesh of Christ which is indeed the Body of life. That manna was from heaven; this is from above the heavens. The former was from heaven, the latter from the Lord of the heavens; the former was subject to corruption if it was preserved for a second day, the latter foreign to all corruption so that whoever shall have piously tasted it will not be able to experience corruption.

For the people of Israel water flowed from the rock; for you Blood flows from Christ. The water satisfied them for a while; the Blood washes you for eternity. The Jew drinks and is thirsty again; when you drink you will not be able to thirst. The former was given as an image; the latter is given as the reality.

If that which you marvel at is an image, how much greater is the reality whose image you marvel at? Listen and learn that what was done for the Fathers was an image: ‘They drank, he says, ‘from the rock following them, and the Rock was Christ; but with many of them God was not pleased, for they were laid low in them desert. These things moreover were done as a type for us’ [1 Cor. 10.4-6]. You have come to know the more excellent things, for the light is more excellent than the shade, reality more excellent than image, the Body of the Giver more excellent than the manna from heaven.
Divine consecration

Perhaps you will say, ‘What I see is different from what you speak of; how is it that you assert that I receive the Body of Christ?’ And so it still remains for us to prove this. And thus we use manifold examples so that we may prove that this is not what nature formed but what the blessing consecrated, and that there is greater power in the blessing than in nature, because by the blessing nature itself is changed

We note, therefore, that grace is more powerful than nature, even when we are only speaking of the grace that comes from the blessing of a prophet. But if a human blessing had such power so as to be able to change nature, what do we say about the divine Consecration itself in which the very words of Our Lord and Saviour are at work? For that Sacrament which you receive is brought about by the word of Christ.

If the word of Elijah had such power as to call down fire from heaven, will not the word of Christ have the power to change the nature of the elements? You have read about the creation of the whole world: ‘He spoke and they were made; he gave a command and they were created’ [Ps. 33.9]. Therefore can not the word of Christ, which was able to create out of nothing that which did not exist, change those things that do exist into that which they were not? To create new things is no lesser thing than to change natures.