"I love how pastoral the catechism is. Those who write off catechisms as dry and dusty, as freeze-dried dogma, have never read this one. Isn't it comforting to know that the Lord's Table is not for those who smile all the time and have great self-esteem, but for those who are 'displeased with themselves because of their sins' (Answer 81)? The Supper is for those with 'continuing weakness' who, although they are seriously flawed, 'desire more and more to strengthen their faith and to lead a better life.'" Kevin DeYoung. The Good News We Almost Forgot. 145.

Question 80: How does the Lord's Supper differ from the Roman Catholic Mass?

Answer: The Lord's Supper declares to us that our sins have been completely forgiven through the one sacrifice of Jesus Christ which He Himself finished on the cross once for all. It also declares to us that the Holy Spirit grafts us into Christ, Who with His very body is now in heaven at the right hand of the Father where we worship Him. But the Mass teaches that the living and the dead do not have their sins forgiven through the suffering of Christ unless Christ is still offered for them daily by the priests. It also teaches that Christ is bodily present in the form of bread and wine where Christ is therefore to be worshipped. Thus the Mass is basically nothing but a denial of the one sacrifice and suffering of Jesus Christ and it is idolatary.

Question 81: Who are to come to the Lord's Table?

Answer: Those who are displeased with themselves because of their sins but who nevertheless trust that their sins are pardoned and that their continuing weakness is covered by the suffering and death of Christ, and who also desire more and more to strengthen their faith and to lead a better life. Hypocrites and those who are unrepentant, however, eat and drink judgment on themselves.  

Question 82: Are those to be admitted to the Lord's Supper who show by what they say and do that they are unbelieving and ungodly?

Answer: No, that would dishonor God's covenant and bring down God's anger upon the congregation. Therefore, according to the instruction of Christ and His apostles, the Christian church is duty bound to exclude such people, by the official use of the keys of the kingdom, until their lives are reformed.