While studying the historical and theological background of the Lord’s Supper (part of which I posted a few days back), I came across this helpful summary of the differences between Rome’s understanding of the Mass and the Reformed understanding of the Lord’s Supper. It is found in Francis Turretin’s Institutes of Elenctic Theology (vol. 3, page 523). I’ve edited it slightly to make it easier to read.
1) In the Lord’s Supper God gives and believers receive. In the Mass the priest gives and God receives.
2) In the Lord’s Supper Christ instituted a monument and remembrance of his sacrifice and death. In the Mass the priest offers Christ to God as a victim for sins.
3) In the Lord’s Supper Christ gave the bread to his disciples and said, ‘Take, eat’ but he did not offer anything to the Father nor did he sacrifice himself in it. In the papal Mass they teach that Christ offers himself as a sacrifice to the Father.
4) In the Lord’s Supper Christ said ‘This do,’ which means, ‘eat and drink.’ In the Mass the Romanists teach ‘This do’ means ‘sacrifice this.’
5) In the Lord’s Supper Christ commanded his disciples to take and eat the bread which he gave them. But in the solitary Mass the priest doesn’t give anything to the people and when no one is present he still says,”Take.’
6) The Lord’s Supper is a commemoration of Christ absent and sitting in heaven at the right hand of God. The Mass is a sacrifice of Christ under the species of the bread and wine.
7) The Supper was instituted in memory of Christ alone and those who can show forth his death. The Mass is celebrated in memory of the saints and for the dead, who cannot do what Christ requires.
More differences could be given, but this is a good starting list. One main point to mention is that in the Lord’s Supper, the focus is primarily on the God-to-man aspect (he feeds and serves us); in the Mass it is primarily a man-to-God movement (the priest offers the sacrifice on the altar). This is one reason the Reformers were so critical of the Mass as being a denial of Christ’s one sacrifice on the cross.
Furthermore, is important to note also that Turretin wasn’t playing around with straw men here. You can read the Council and Canons of Trent and the modern-day Roman Catholic Catechism to see what they still teach and see that Turretin understood what Rome taught. In this section of his Institutes, he refuted the papal Mass quite well using biblical, theological, historical, and reasonable arguments. Turretin is a great place to go to get an in-depth discussion and refutation of Rome’s unbiblical teaching of the Mass from a Reformation point of view.