The Eucharist is important because its name (‘Eucharist’ is Greek for ‘thanksgiving’) refers to the act of Jesus giving God thanks for the bread and wine.
The Eucharist serves several functions across denominations: it reminds participants of God’s saving acts including the Passover and Jesus’ sacrifice, it orients them to a positive future: the coming of Jesus (I Cor 11:26), it affirms individual faith as a personal reminder of salvation and it strengthens community as it is practiced in the Church.
Catholic theology views the eucharist in terms of transubstantiation: the bread and wine are transformed into the body and blood of Christ as a result of their priestly consecration, affirmed by the 4th Lateran Council (13th c.).
The ‘accidents’ (the outward appearance) and ‘substance’ (the inner reality) of the bread and wine were thought to become the same in transubstantiation.
Edward Schillebeeckx introduced ‘transignification’, the idea that what changes at the point of consecration is the significance of the bread and wine to the believer.
Luther, with Sola Scriptura, dismissed using Greek categories of thought to define the Eucharist; he believed Jesus was present, but how was a mystery.
The ‘is’ in ‘This is my body’ is not to be taken literally but means ‘signifies’ in Zwingli’s approach, called memorialism, which puts the focus not on the elements themselves, but on the act of remembering.
‘Virtualism’ in Calvinism says that though the elements remain unchanged at consecration, believers receive virtue or power through their participation.