What are key differences in how the Eucharist is viewed across the major groups under Christianity?

The Orthodox Church holds that the Divine Liturgy truly makes present the one sacrifice of Christ, and that the bread and wine become the actual Body and Blood of Christ through the descent of the Holy Spirit (cf. John 6:53‑56; St. John Chrysostom, On the Priesthood 3.4). This change is a mystery, not a philosophical explanation, and the faithful receive communion for the forgiveness of sins and eternal life (cf. Liturgy of St. Basil, Prayer of the Faithful). The Roman Catholic Church likewise teaches transubstantiation, affirming that the substance of the bread and wine is changed into the Body and Blood of Christ while the accidents remain (Council of Trent, Session XIII). It emphasizes the sacrificial nature of the Mass as a re‑presentation of Christ’s once‑for‑all offering. Most Protestant traditions reject a real change in the elements, viewing the Lord’s Supper as a memorial or spiritual communion (e.g., Luther’s sacramental union, Calvin’s spiritual presence, Zwingli’s symbolic remembrance), and they generally do not regard the Eucharist as a sacrifice. As the Orthodox Fathers warn, separating the sign from the reality leads to a loss of the mystery’s saving power (cf. St. Ignatius of Antioch, Letter to the Smyrneans 7).