13 What more after the heads of dragons? For those dragons have their chief, and he is himself the first great dragon. And concerning him what has He done that has wrought Salvation in the midst of the earth? Hear: “You have broken the head of the dragon”. Of what dragon? We understand by dragons all the demons that war under the devil: what single dragon then, whose head was broken, but the devil himself ought we to understand? What with him has He done? “You have broken the head of the dragon.”
That is, the beginning of sin. That head is the part which received the curse, to wit that the seed of Eve should mark the head of the serpent. For the Church was admonished to shun the beginning of sin. Which is that beginning of sin, like the head of a serpent? The beginning of all sin is pride. There has been broken therefore the head of the dragon, has been broken pride diabolical. And what with him has He done, that has wrought Salvation in the midst of the earth? “You have given him for a morsel to the Ethiopian peoples.”
What is this? How do I understand the Ethiopian peoples? How but by these all nations? And properly by black men: for Ethiopians are black. They are themselves called to the faith who were black; the very same indeed, so that there is said to them, “for you were sometime darkness, but now light in the Lord.”...Thence was also that calf which the people worshipped, unbelieving, apostate, seeking the gods of the Egyptians, forsaking Him who had delivered them from the slavery of the Egyptians: whence there was enacted that great Sacrament.
For when Moses was thus angry with them worshipping and adoring the idol, and, inflamed with zeal for God, was punishing temporally, in order that he might terrify them to shun death everlasting; yet the head itself of the calf he cast into the fire, and ground to powder, destroyed, scattered on the water, and gave to the people to drink: so there was enacted a great Sacrament. O anger prophetic, and mind not perturbed but enlightened! He did what? Cast it into the fire, in order that first the form itself may be obliterated; piece by piece grind it down, in order that little by little it may be consumed: cast it into the water, give to the people to drink!
What is this but that the worshippers of the devil had become the body of the same? In the same manner as men confessing Christ become the Body of Christ; so that to them is said, “but you are the Body of Christ and the members.” The body of the devil was to be consumed, and that too by Israelites was to be consumed. For out of that people were the Apostles, out of that people the first Church....Thus the devil is being consumed with the loss of his members. This was figured also in the serpent of Moses.
For the magicians did likewise, and casting down their rods they exhibited serpents: but the serpent of Moses swallowed up the rods of all those magicians. Let there be perceived therefore even now the body of the devil: this is what is coming to pass, he is being devoured by the Gentiles who have believed, he has become meat for the Ethiopian peoples. This again, may be perceived in, “You have given him for meat to the Ethiopian peoples,” how that now all men bite him. What is, bite him?
By reproving, blaming, accusing. Just as has been said, by way of prohibition indeed, but yet the idea expressed: “but if you bite and eat up one another, take heed that you be not consumed of one another.” What is, bite and eat up one another? You go to law with one another, you detract from one another, you heap revilings upon one another. Observe therefore now how that with these bitings the devil is being consumed. What man, when angry with his servant, even a heathen, would not say to him, Satan? Behold the devil given for meat. This says Christian, this says Jew, this says heathen: him he worships, and with him he curses!...
Source: The Enarrations, or Expositions, on the Psalms (New Advent)