The Editor asks me to write on ‘the nature of sacrifice, showing how the Mass is a sacrifice’. It sounds quite simple. It is as if I were asked to speak on the nature of buttercup, and show that the flower you have picked is a butter-cup. I can get a dictionary description of Buttercup, show you Pictures of the species of Ranunculus called buttercup, compare your specimen with these descriptions and pictures, prove to you that there is no difference whatever between them, and conclude without a shadow of a doubt that you have picked an authentic, genuine sample of the class ‘Buttercup’.
We might proceed in the same way with this present assignment. We might look up the word ‘Sacrifice’ in a standard dictionary; or start from some good definition of ‘Sacrifice’ from some Doctor of the Church. Then we could take a good look at what happens at Mass, show how it fits the definition, and conclude that Holy Mass is undoubtedly a genuine specimen of the class ‘Sacrifice’.