Why does the Catholic Church “police” who can receive the Eucharist? After all, many Protestant churches practice “open communion,” in which the Lord’s Supper is offered to all baptized Christians in attendance, or to all believers (including the unbaptized), or simply to whoever wishes to receive.

But as a non-Catholic attending a Catholic Mass quickly discovers, this is not the case in reverse: non-Catholics are (typically) not permitted to receive. And Catholics are themselves reminded that “a person who is conscious of grave sin” may not “receive the body of the Lord without previous sacramental confession unless there is a grave reason and there is no opportunity to confess” (CIC 916). And ministers of Holy Communion are instructed that those who have been excommunicated or are otherwise “obstinately persevering in manifest grave sin are not to be admitted to holy communion” (915).

On the surface, it’s easy to see why the Catholic practice of “closed communion” appears scandalous and pharisaical. After all, when “the tax collectors and sinners were all drawing near to hear” Jesus, it’s the hypocritical Pharisees who complain that “this man receives sinners and eats with them” (Luke 15:1-2). If Jesus dined with sinners, then why do we refuse them the Lord’s Supper?

The answer is because Jesus treats the Last Supper differently. For starters, whereas Jesus dined with others quite freely, the Last Supper is presented in the Gospels as a more exclusive affair, between Jesus and his chosen twelve. St. Matthew says that Jesus “sat at table with the twelve disciples,” and St. Luke describes how Jesus said to them, “You are those who have continued with me in my trials; as my Father appointed a kingdom for me, so do I appoint for you that you may eat and drink at my table in my kingdom, and sit on thrones judging the twelve tribes of Israel” (22:28-30).

This is a special, intimate moment between Jesus and his closest followers. Jesus tells them, “I have earnestly desired to eat this passover with you before I suffer” (Luke 22:15). This Jewish context is significant, since the Passover was a decidedly “closed” affair: “When a stranger shall sojourn with you and would keep the passover to the Lord, let all his males be circumcised, then he may come near and keep it; he shall be as a native of the land. But no uncircumcised person shall eat of it” (Exod. 12:48). In other words, anyone was free to join the Passover table . . . as long as he first entered the covenant people through circumcision.

It’s not only that the Last Supper is an intimate affair between Jesus and his disciples, or that it’s the fulfillment of the Jewish Passover. It’s also that the Eucharist is communion with Jesus Christ. This is why Catholics, who believe that the Eucharist really is Jesus, treat the Eucharist with more reverence, and in a more exclusive manner, than those Christians who believe it’s only a symbol. We take seriously St. Paul’s warning that whoever “eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty of profaning the body and blood of the Lord,” and that “any one who eats and drinks without discerning the body eats and drinks judgment upon himself” (1 Cor. 11:27,29).

Christians treat hospitality (open to all!) very differently from how they treat marital intimacy (reserved for the one with whom you’re in a covenantal relationship!). So which of these is the Eucharist more like? If you think the Eucharist is just a symbol, you might think the former. But Scripture is clear that it’s the latter. St. Paul takes the words of Genesis 2:24, about how “the two shall become one flesh” in sexual union, and applies them to the union of Christ and the Church (Eph. 5:31-32). And how does this union occur? As Paul explains, “the cup of blessing which we bless, is it not a participation in the blood of Christ? The bread which we break, is it not a participation in the body of Christ?” And Paul insists that “we who are many are one body, for we all partake of the one bread” (1 Cor. 10:16-17). In other words, Christ and the Church become one body through the Eucharist.

St. Justin Martyr told us all of this back in about the year 160, writing,

And this food is called among us Εὐχαριστία [the Eucharist], of which no one is allowed to partake but the man who believes that the things which we teach are true, and who has been washed with the washing that is for the remission of sins, and unto regeneration, and who is so living as Christ has enjoined. For not as common bread and common drink do we receive these; but in like manner as Jesus Christ our Savior, having been made flesh by the Word of God, had both flesh and blood for our salvation, so likewise have we been taught that the food which is blessed by the prayer of his word, and from which our blood and flesh by transmutation are nourished, is the flesh and blood of that Jesus who was made flesh.

So the earliest Christians didn’t practice open communion. They required anyone presenting themselves for the Eucharist to be (1) baptized, (2) a believing Catholic, and (3) not living in sin. Why? Because, as Justin says, the earliest Christians realized that the Eucharist isn’t common food and drink, but truly the flesh and blood of Jesus. So seriously did the early Christians take this guarding of the Eucharist that “in the early Church, the catechumens, or hearers who had not yet been baptized, were dismissed at the conclusion of the Liturgy of the Catechumens, and the faithful, or baptized Christians, remained to celebrate the mystery of the Eucharist.”

But what about Judas? It’s all well and good to say, as the Eastern Liturgy does, “Holy things for holy people.” But at that first Eucharist, we find Judas Iscariot. Benjamin Perry, a Protestant minister at Middle Church in New York City (“where therapy meets Broadway”), puts the argument this way:

Do not deny anyone communion. Ever.

Communion is not a reward. It is not a privilege for the righteous. It is an invitation to step towards God’s table where everyone has enough and everyone a place.

Remember: Jesus fed Judas.

How do we make sense of this? For starters, it’s not entirely clear that Jesus did give the Eucharist to Judas, and the early Christians disagreed on this point. Nevertheless, the majority opinion is that he probably did, and for good reason: Judas’s sin was a secret. As St. Thomas Aquinas explains, “Christ did not repel Judas from Communion so as to furnish an example that such secret sinners are not to be repelled by other priests.”

This is an important distinction. Take the case of two people who commit adultery. One of them repents and goes to confession; the other doesn’t. If the priest knows about the adultery only through the confessional, he may not deny the unrepentant sinner Communion, since to do so would be to reveal this secret sin. Similarly, “if your brother sins against you,” you should first “go and tell him his fault, between you and him alone. If he listens to you, you have gained your brother” (Matt. 18:15). People should have the space to quietly repent without being publicly humiliated.  But none of that applies when the person is openly non-Catholic, either in creed or in action. That’s why canon 915 says you deny Communion in cases of “manifest grave sin”—the sin has to be out in the open.

In the case of Judas, we see these principles at play. Initially, Aquinas points out, “the wickedness of Judas was known to Christ as God; but it was unknown to him after the manner in which men know it.” Jesus doesn’t want to reveal his secret sin publicly, and so he instead says, “Truly, I say to you, one of you will betray me.” His disciples, including Judas, then ask, “Is it I, Lord?” (Matt. 26:20-25). Jesus has given Judas one last chance to convert without naming him openly. In so doing, he’s also pricked the consciences of the other disciples, who aren’t confident it won’t be they who betray Jesus. It’s only once Judas’s sin becomes manifest, when he’s openly betraying Jesus, that Jesus rebukes him openly: “Judas, would you betray the Son of man with a kiss?” (Luke 22:48).

This is the model the Church has sought to follow for the past two thousand years. If the person’s sin is private, handle the issue privately (including by instructing him not to present himself for Communion); if the person’s sin is open, then prevent scandal by refusing to allow him to eat and drink “judgment upon himself.”