Lord's Day 30

Q. 80.  What difference is there between the Lord’s Supper and the popish mass?
A.  The Lord’s Supper testifies to us that we have a full pardon of all sin by the only sacrifice of Jesus Christ, which He Himself has once accomplished on the cross;1 and that we by the Holy Ghost are ingrafted into Christ,2 who according to His human nature is now not on earth, but in heaven at the right hand of God His Father,3 and will there be worshiped by us4—but the mass teaches that the living and dead have not the pardon of sins through the sufferings of Christ, unless Christ is also daily offered for them by the priests; and further, that Christ is bodily under the form of bread and wine, and therefore is to be worshiped in them; so that the mass, at bottom, is nothing else than a denial of the one sacrifice and sufferings of Jesus Christ, and an accursed idolatry.5

Q. 81.  For whom is the Lord’s Supper instituted?
A.  For those who are truly sorrowful for their sins,6 and yet trust that these are forgiven them for the sake of Christ, and that their remaining infirmities are covered by His passion and death;7 and who also earnestly desire to have their faith more and more strengthened, and their lives more holy;8 but hypocrites, and such as turn not to God with sincere hearts, eat and drink judgment to themselves.9 

Q. 82.  Are they also to be admitted to this supper, who, by confession and life, declare themselves unbelieving and ungodly?
A.  No; for by this the covenant of God would be profaned, and His wrath kindled against the whole congregation;10 therefore it is the duty of the Christian church, according to the appointment of Christ and His apostles, to exclude such persons,11 by the keys of the kingdom of heaven, till they show amendment of life.