Question: "Should communion be open or closed?"
Answer: The Bible's teaching on Communion, or the Lord's Supper, is found in 1 Corinthians 11:17-34 and promotes "open" participation for believers. All those who are true believers in God through personal faith in Jesus Christ, His Son, are worthy to partake of the Lord's Supper by virtue of the fact they have accepted the death of Christ as payment for their sins (see also Ephesians 1:6-7).
The actual reasoning behind some churches practicing "closed" communion seems to be that they want to make sure everyone partaking is a believer. This is understandable; however, it places church leadership and/or church ushers in a position of determining who is worthy to partake, which is problematic at best. A given church may assume that all of their official members are true believers, but even this is not necessarily always true.
The practice of restricting communion to church members seems to be an attempt to make sure someone doesn't partake in an unworthy manner, which some assume to mean that person is not a true Christian. However, the word is not “unworthy” but is “unworthily.” This is referring to the manner in which a person partakes of the bread and cup, not to his or her worthiness to participate in the first place. No one is really worthy to come into the presence of God for any reason, but by virtue of the shed blood of Christ on the cross, all who believe in Him have been made worthy. 1 Corinthians 11:27-32 is clearly addressed to believers, not unbelievers. Beginning this passage in verse 23, it is obvious Paul is talking about believers partaking of the Lord's Supper and thus they "proclaim the Lord's death till He comes" (verse 26). Also, Paul concludes the passage by calling the readers "brethren" (verse 33). Therefore, the passage is warning believers to avoid partaking in an unworthy manner. This unworthy manner is described as excluding others when you come to communion and partaking of the elements to curb one's hunger (verse 34).
So, communion should be "open" to all believers, but those believers should examine their motive for partaking. If believers are irreverent in their attitude toward communion because of prejudice or appetite, they should voluntarily refuse to partake, or, in some extreme cases, should be counseled by church leadership not to partake. May the Lord bless you in understanding the Biblical message and meaning of communion, so the practice can be a real blessing to you.