1. The Church of the medieval period, of the later Middle Ages, espoused the doctrine of Saint Thomas Aquinas, the Thomistic doctrine, that the Eucharistic Consecration caused the substances of bread and wine to be destroyed and replaced by the substances of the Body and Blood of Christ, hence the corrective offered by the Church of England in Article of Religion XXVIII in which it is said that Transubstantiation 'overthrows the nature of a sacrament.' The immediate reason: unfortunately, the late medieval Church had ceased properly to understand Saint Thomas's meaning of substance as a non-material essence and saw 'substance' as materiality. If the material substances of bread and wine (which is what is specifically targeted in the Article) cease to exist, the outward and visible sign of the Blessed Sacrament is vitiated and the Sacrament does not exist.
2. The Eucharistic Change, or transformation of the bread and wine into Our Lord's Body and Blood by the Word of Christ and the Invocation of the Holy Ghost, is a true and literal Change, for one objective thing (the elements) becomes another objective Thing (Our Lord), but it is not a material change - the Change occurs on the supernatural and metaphysical, the supramaterial, level, inaccessible to our understanding and perception.
3. In Saint John 6, Our Lord uses a reference to the 'gnawing' and 'chewing' of His Flesh and Blood - and He is unwilling to reduce His teaching to a metaphor or analogy. Our Lord intended the Bread of Life discourse to be taken literally, which indeed it was, as was demonstrated by the reaction of the crowd.
4. There is also the quintessential point of presenting Holy Scripture and the teaching of the Church Fathers in their proper context, and we are called to exegesis, to bring out the actual meaning of the text, rather than eisigesis, the attempt to infuse a preconceived notion into the text. The contextual reading of the Scriptures itself provides the fullest warrant for belief in the Real Objective Presence. As one has brilliantly pointed out, affirming the sacramental principle in opposition to gnosticism, 'Our Lord would not instruct us to do this and then not give us a way of accomplishing it.' Contextual reading of the Bible is the key to all of Catholic doctrine.
5. The examination of the Old Testament is all-important: the divine institution by YHWH in ancient Israel of covenant sacrifice, priesthood, liturgical worship, the use of bread and wine sacramentally and the centrality of the Lamb. The Todah sacrifice, the Eucharistic or Thank Offering of bread and wine in the Old Covenant, is an absolutely essential reference - and it is vital to recognise it. References to Melchizedek, the showbread, the manna and the Passover all prove the continuity of the Eucharist with the Old Testament.
6. The axiom for the proper Catholic interpretation of Scripture: the Mass and Catholic Priesthood are the fulfillment of the Old Testament sacramental and sacrificial system, as Our Lord Jesus Christ is the unique embodiment, personification and fulfilment of Israel and the Old Covenant. The Eucharist is the perfection and accomplishment, the full manifestation, of that to which the old sacrifices and sacraments gave symbolism, sign and foretaste. There is a hermeneutic of continuity, not rupture, between the Old and New Testaments, or as Saint Augustine saith, 'The Old Testament is the New Testament concealed, the New Testament is the Old Testament revealed.' Christ is the final and full revelation of what was conveyed in the Old Covenant in prefigure and shadow. Jesus Christ is the true Priest, Victim, Sacrifice and Altar, the Lamb, truly made present in the celebration of the Mass, and under the form of bread and wine.
7. There is an inseparable link between Holy Scripture and Holy Tradition; we invoke the magisterial Church Fathers of the first millennium to demonstrate the unchanging and perennial teaching of the Church on the Real Presence, a doctrine indisputable when consulting the faith and practice of the Church in the patristic era: true Catholicism is inherently patristic and liturgical, and looks to the sources, ad fontes, ressourcement, when seeking to present the substance of that Faith Once Delivered to the Saints and faithfully transmitted by the Church of the Apostles and Fathers.
