But that wasn’t what was said in
the article you cited. Scott Diekmann, the author of the article, made an explicit simile between the unity of the bread and the body of Christ, the wine and the blood of Christ: “
Just as Christ’s unchanged human and divine natures are inseparably united, so the natural bread and Christ’s true natural body are united (likewise the wine and the blood).” Unless there is a subject that keeps these united, and takes on their natures (that is, becomes the
subject both of the bread/wine and the body/blood of Christ), then that simile fails. If Diekmann wants to hold on to this simile – that the bread/wine and the body/blood of Christ is united
just as “Christ’s unchanged human and divine natures are inseparably united” – then he must either affirm impanation or say that someone or something else than Christ is the subject of Christ’s body and blood. (At least as long as the sacrament is in existence.)
Of course the sane thing would be to just trash the simile.
And the same is true of the incarnation, yet I would be very surprised if Diekmann has a problem with the use of ousia/homoousious in the Nicene Creed. Transubstantiation has never been an explanation of how the Eucharist comes into being.
But why, exactly? And why was it OK to dogmatise philosophical language in 325, yet not so in 1215?