These two statements, I think, lead to the following conclusion. Faced with a disbeliever – either a Protestant (Calvinist?) who says No, it’s only a memorial ceremony, or an atheist who says it’s not even that – the word “transubstantiation” doesn’t provide you, as far as I can see, with any argument that would help you to answer their questions such as, How does it work?
Well, the word metabolism doesn’t provide one, as far as I can see, with how metabolism works. The definition in the dictionary gives a general idea of what it refers too, a biological or physiological process. The etymology of metabolism (from etymolonline) comes from ‘meta-’ change + ‘ballein’ to throw. Not much to go on here. In this sense, I think the word transubstantiation from its latin roots is more meaningful as it essentially means a change of substance and more specifically a change of the whole substance into another substance as this was the meaning giving to the word by the theologians when it appeared in eucharistic theology.
As you say, to explain how metabolism works, one can’t just use the word ‘metabolism’ but needs to introduce other words and terms. Transubstantiation works by divine power and not according to the laws of nature and this is implicitly contained in the first sentence you quote from me.
What is going on beneath the surface?
Transubstantiation, i.e., a change of the whole substance of the bread into the substance of the body of Christ and the whole substance of the wine into the substance of the blood of Christ. The substance (from latin substare ‘to stand under’) is that which ‘stands under’ as it were the sensible ‘species’. ‘Species’ is a latin word which is translated ‘appearances.’ Species is the word the Church uses in its official terminology concerning what remains of the bread and wine after the change of the substances of the bread and wine. Species means the same thing as the ‘accidents’ in scholastic Aristotelian philosophical language. The change going on here at the substance level is metaphysical, i.e., beyond sense observation and sense phenomena unlike metabolism.
How do you know what you say is true?
Faith in the word of Jesus who is God and Truth itself as he himself declared ‘I am the Way, the Truth, and the Life.’ We believe that the bread and wine are transubstantiated into the true body and the true blood of Christ solely on the words of Jesus ‘This is my body…This is my blood’, the Bread of Life discourse in the gospel of John, and drawing an analogy between the figures in the Old Testament of the eucharist and the eucharistic sacrifice such as the sacrifice of the Passover Lamb, the Manna in the desert. We cannot prove by sense phenomena or sight that Jesus’ true body and true blood is in the eucharist ordinarily, I say ordinarily because there are a few eucharistic miracles in which blood or tissue is seen. Believing in the Real Presence of Christ’s true body and true blood in the eucharist which comes about by the transubstantiation of the bread and wine is an act of the virtue of faith which is meritorious.