But in the following instructions I do not commend you, because when you come together it is not for the better but for the worse. For, in the first place, when you come together as a church, I hear that there are divisions among you. And I believe it in part, for there must be factions among you in order that those who are genuine among you may be recognized. When you come together, it is not the Lord's supper that you eat. For in eating, each one goes ahead with his own meal. One goes hungry, another gets drunk. What! Do you not have houses to eat and drink in? Or do you despise the church of God and humiliate those who have nothing? What shall I say to you? Shall I commend you in this? No, I will not. For I received from the Lord what I also delivered to you, that the Lord Jesus on the night when he was betrayed took bread, and when he had given thanks, he broke it, and said, “This is my body which is for you. Do this in remembrance of me.” In the same way also he took the cup, after supper, saying, “This cup is the new covenant in my blood. Do this, as often as you drink it, in remembrance of me.” For as often as you eat this bread and drink the cup, you proclaim the Lord's death until he comes. Whoever, therefore, eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty concerning the body and blood of the Lord. Let a person examine himself, then, and so eat of the bread and drink of the cup. For anyone who eats and drinks without discerning the body eats and drinks judgment on himself. That is why many of you are weak and ill, and some have died. But if we judged ourselves truly, we would not be judged. But when we are judged by the Lord, we are disciplined so that we may not be condemned along with the world. So then, my brothers, when you come together to eat, wait for one another—if anyone is hungry, let him eat at home—so that when you come together it will not be for judgment. About the other things I will give directions when I come. (1 Corinthians 11:17-34 ESV)There have been a variety of interpretations as to what it means to discern the Lord's body. There are some significant textual variants in this passage and I don't necessarily agree with the textual decisions made by the ESV translators but I don't believe these textual variants are significant in how the passage should be interpreted. Older interpretations tended to understand "discerning the body" sacramentally. Those in Corinth were not recognizing that they were receiving the body and blood of the Lord, were treating it as a common meal, and were not showing proper reverence. More recent interpretations direct us to the actual abuses that were taking place and argue that "discerning the body" has more to do with showing love towards our brothers and sisters in Christ since they are the body of Christ.
Both ways of interpreting the passage don't seem to take everything that is said seriously enough. Paul is not addressing a congregation that is explicitly denying that we receive Christ's body and blood in the Lord's Supper. But if "discerning the body" only has to do with our treatment of our brothers and sisters in Christ, then it doesn't make much sense as to why the unworthy partaker is "guilty concerning the body and blood of the Lord." A few years ago I started thinking that there is probably a double entendre here. By treating the Lord's Supper as a common meal and making the poor people sit at the kiddie table, they were by their actions denying that receiving Christ's body in the sacrament is what it's all about and also not acknowledging their brothers and sisters in Christ as brothers and sisters in Christ. They were neither discerning Christ's body in the sacrament nor discerning that every member of the church is part of Christ's body. They were not engaging in a communal participation in the body and blood of Christ but engaging in a common feast with other wealthy people.
Recently, I've been listening to a Bible study on the Gospel of Mark led by Dr. James Voelz. In one of the classes, Dr. Voelz suggests an interpretation that is just a little bit different from my own and I think a better option. Dr. Voelz argues that "the body" which is not being discerned is the body of Christ which is in the body of the fellow communicant. When we partake of communion we receive Christ's actual body and blood inside of us. If we despise those we commune with we are not recognizing the body and blood of Christ inside of them. By despising our brothers and sisters in Christ and thinking we are better than them, we become unworthy participants and completely miss the point. We end up eating and drinking judgment to ourselves. Christ gives His body and blood for sinners. When we receive Christ's body and blood we are testifying that we are sinners and that we need the forgiveness of sins given in His body and blood. But if in some way we use the Supper to show that we are better than others who receive the Supper we do not know what we are truly receiving. Because of this sin against the body and blood of Christ, Paul says that some were actually getting sick and even dying. I've heard some try to explain that this was just the natural result of overeating but that's not what Paul says.
Paul's commentary on the Words of Institution found in this chapter should be enough to convince us that we truly receive the body and blood of Christ in the Lord's Supper and that it is Christ's body and blood regardless of whether or not people believe that it is. Those who do not discern the body still receive the body but it is to their own judgment.
This should be enough to keep anyone from adopting an open communion policy as well. That's not the issue Paul is actually addressing. Paul is dealing with those who deny the body of Christ in their brothers by their actions. But today we have many who just plain deny the presence of the body of Christ. There are many confessions of faith and church bodies that officially deny the body of Christ. It would be unloving to encourage people who do not discern the body of Christ in the Supper to partake of something that could hurt them. The church has always practiced closed communion. It's not until very recently that some have begun to practiced open communion. In the early church you couldn't just walk in and expect to be able to partake. The bishop had to know you. Travelers had to bring a note from their bishop. To partake of communion with others meant that you shared a common confession with them.
On the other hand, the passage warns against being too exclusive. If those who hold to a common confession are excluded, the person excluding them fails to discern the body of Christ that is in the one they are excluding. People shouldn't have to jump through hoops and receive the Lord's Supper as some kind of reward.