The table's door
Who may come to the Supper, and what unworthy participation is.
1 Corinthians 11:27-34
27Therefore whoever eats this bread or drinks the Lord’s cup in a way unworthy of the Lord will be guilty of the body and the blood of the Lord.
28But let a man examine himself, and so let him eat of the bread, and drink of the cup.
29For he who eats and drinks in an unworthy way eats and drinks judgment to himself if he doesn’t discern the Lord’s body.
30For this cause many among you are weak and sickly, and not a few sleep.
31For if we discerned ourselves, we wouldn’t be judged.
32But when we are judged, we are punished by the Lord, that we may not be condemned with the world.
33Therefore, my brothers, when you come together to eat, wait for one another.
34But if anyone is hungry, let him eat at home, lest your coming together be for judgment. The rest I will set in order whenever I come.
What each tradition says
Rabbinic / Midrashic
Kaufmann Kohler defines the Agape as the name for the communion meals of the early Christians. At these meals, rich and poor, master and slave, sat together at one table, merging all distinctions of rank in fraternal union and fellowship.
Kaufmann Kohler, Agape (Love-feasts) (Jewish Encyclopedia, 1901-1906) — Opening definition of the Agape
Patristic
The Didache says no one may eat or drink of the Thanksgiving (Eucharist) except those who have been baptized into the name of the Lord. It adds that the Lord also said, “Give not that which is holy to the dogs.”
The Didache (Teaching of the Twelve Apostles), The Teaching of the Twelve Apostles, ch. 9 (ANF vol. 7, ed. Roberts & Donaldson) — Ch. 9:5 — who may eat of the Eucharist
Catholic
Thomas Aquinas distinguishes among sinners: some are secret, while others are notorious, whether by evidence of the fact, such as public usurers or robbers, or by being denounced as evil by an ecclesiastical or civil tribunal. He concludes that Holy Communion ought not to be given to open sinners when they ask for it.
Thomas Aquinas, Summa Theologica, Third Part, Q. 80, Art. 6 (trans. Fathers of the English Dominican Province) — ST III, Q. 80, Art. 6 ('Whether the priest ought to deny the body of Christ to the sinner seeking it?') — the Reply
Orthodox
Chrysostom says a person eats judgment to himself by not discerning the Lord’s body. This means not searching or bearing in mind, as he ought, the greatness of the things set before him, and not estimating the weight of the gift.
John Chrysostom, Homilies on the First Epistle to the Corinthians, Homily XXVIII (NPNF ser. 1, vol. 12, trans. T. W. Chambers) — Homily XXVIII, on 1 Cor 11:28-29 ('not discerning the Lord's body')
Reformed / Protestant
Calvin says to eat unworthily is to pervert the pure and right use of it by abusing it. There are various degrees of this unworthiness: some offend more grievously, others less. A fornicator, perjurer, drunkard, or cheat intrudes without repentance.
John Calvin, Commentary on the Epistles of Paul the Apostle to the Corinthians, vol. 1 (trans. John Pringle; Calvin Translation Society) — Commentary on 1 Corinthians 11:27 ('whosoever shall eat this bread... unworthily')
Evangelical
Wesley says whoever eats this bread unworthily eats in an unworthy, irreverent manner, without regarding either Him who appointed it or the design of its appointment. Such a person is guilty of profaning that which represents the body and blood of the Lord.
John Wesley, Explanatory Notes upon the New Testament — Notes on 1 Corinthians 11:27 ('Whosoever shall eat this bread unworthily')