“…discipline is, in all Churches, that which concerns participation in the Lord's Supper. Questions 81 and 82 deal with this. The first question is: who can and must participate in the Supper? The answer is very beautiful: the Lord's table is for those who are not worthy of it. Jesus had said it: it is not the healthy who need a doctor, but the sick; it is not the righteous who have hunger and thirst for the justice of God, but sinners. Jesus himself gave the example: He celebrated his first (and last) Supper with the Twelve—with Judas, who had already betrayed Him, with Peter, who would deny Him, and with all the others, who, giving themselves over to flight, would abandon Him. The table of Jesus is a banquet of sinners. It is in their midst that Jesus dwells, it is with them that He eats, to change their hearts and bring new life.
Therefore, to the question: «Who must participate in the Supper?» the first answer is: sinners. But there is a second answer, equally important: these sinners invited to the table of Christ must be «displeased with themselves», that is, they must be sinners who are nonetheless repentant, absolutely confident in the mercy of God, and also desirous of growing in the Christian faith and improving the quality of their lives.
Whoever, on the other hand, does not feel this desire—because they are satisfied with themselves and retain they have no need to change anything important in their life, has nothing to repent for and fundamentally doesn’t feel themselves a sinner, it’s better they don’t participates in the Supper. It would be nothing more than a formality, an external act without true internal resonance, a communion more apparent than real. Perhaps the day will come when they will no longer be content with their own righteousness and will hunger and thirst for the righteousness of God. On that day, let them hasten to the table of sinners. For only those who hunger will be satisfied."
-Paolo Ricca’s commentary upon Question 81 of the Heidelberg Catechism.