1 Corinthians 11:26-30 (NASB) For as often as you eat this bread and drink the cup, you proclaim the Lord's death until He comes. Therefore whoever eats the bread or drinks the cup of the Lord in an unworthy manner, shall be guilty of the body and the blood of the Lord. But a man must examine himself, and in so doing he is to eat of the bread and drink of the cup. For he who eats and drinks, eats and drinks judgment to himself if he does not judge the body rightly. For this reason many among you are weak and sick, and a number sleep.
If in Paul's times an ordinary abuse of the Supper could kindle the wrath of God against the Corinthians so that He punished them so severely, what ought we to think as to the state of matters at the present day? We see, throughout the whole extent of Popery, not merely horrid profanations of the Supper, but even a sacrilegious abomination set up in its place!
It is prostituted to filthy lucre and merchandise (1 Timothy 3:8).
It is maimed, by taking away the use of the cup.
It is changed into another aspect by its having become customary for one to partake of his own feast separately, participation being done away.
There is there no explanation of the meaning of the sacrament, but a mumbling that would accord better with a magical incantation, or the detestable sacrifices of the Gentiles, than with our Lord's institution.
There is an endless number of ceremonies, abounding partly with trifles, partly with superstition, and consequently manifest pollutions.
There is the diabolical invention of sacrifice, which contains an impious blasphemy against the death of Christ.
It is fitted to intoxicate miserable men with carnal confidence, while they present it to God as if it were an expiation, and think that by this charm they drive off everything hurtful—and that without faith and repentance. Nay more, while they trust that they are armed against the devil and death, and are fortified against God by a sure defense, they venture to sin with much more freedom, and become more obstinate.
An idol is there adored in the room of Christ.
In short, it is filled with all kinds of abomination.
Taken from Calvin's commentary on 1 Corinthians 11:30.