I got to thinking about the idea of closed vs. open communion today for a couple of reasons. It is an issue that is pretty settled in a lot of the church but settled incorrectly in my view and it needs to be challenged as it exists and debunked for the damage it does.
Our religious culture, taking cues from Rome, for the most part has a default position of suspicion and presumption of guilt when someone new comes to the Table. You must first prove your worth to an authority figure in a local church prior to coming to the Table and being allowed to partake. Of course the easiest way to do that is to "join" a local church, a pragmatic mechanism put in place to substitute for actual relationships but one that leaves little room for people who are visiting or who are not interested in being shackled to an extra-biblical "covenant".
In contrast to how our religious culture approaches our ritualized version of communion, the Bible teaches that the proper stance of the church toward other believers desiring to come to the Lord's Supper is to welcome them unless something they do necessitates that we don't welcome them. The burden is on the church to show why someone should not be welcomed to the table and the standard is a very stringent one. Like our legal system, other believers are "innocent until proven guilty" rather than the reverse.
In other words, a fellow professing believer is not disqualified from the Supper because they are not a "member" of your congregation. Since gatherings that look even vaguely like your local church didn't exist for hundreds of years after the Cross and formal church membership is not commanded, implied or even inferred in Scripture, it is silly to demand that any other believer meet the extra-biblical standard of "joining your church" before you will permit them to partake of something that the Lord commanded His followers do.
In fact I would suggest that it is a greater sin, a far greater and more dangerous sin, to stand between a believer seeking to carry out the commands of our Lord than it is to risk someone who is not eligible partaking of the supper.To put it more succinctly, the damage done by denying the Supper to a brother is far worse than an ineligible person being inadvertently welcomed to the Table.
As someone has been simultaneously told that we are welcome in a gathering but unwelcome in an observance of the Supper, this is an open wound. You are no more justified in refusing fellowship with another believer apart from an unrepentant sin than you are in denying them the Table.
So why is "closed" or even "close" communion so common? As mentioned I think a lot of it is tradition that is a holdover from Roman Catholicism where the ability to deny the demi-salvific nature of the "Mass" is a key tool to control and compel people. That need to control and compel is not unique to Rome and has been Protestantized by countless evangelical groups over the centuries who follow the lead of the Roman hierarchy in taking a sign of love, fellowship and unity and turning it into a club to demand obedience. Another key factor is the general distrust of clergy for the testimony and profession of believers from other traditions. "Oh you were baptized in a Pentecostal church? You probably aren't really saved then. Take our membership classes and affirm our statement of faith and then get back to me, maybe you can come to the communion service next quarter (provided the church votes to accept you as a member, of course)." Pastors are awfully untrusting of other Christians from inside their own tradition, thus the jealous guarding of "their" pulpit. That is exponentially true of Christians in other traditions. So when you combine tradition, control and (to be honest) contempt, you end up with a lot of people being prevented from following the commands of Scripture by the men who of all people should know better.
It is not your Table. It is not my Supper. It is His. He makes the guest list. He tells us who can be excluded (and it is a short list). He commands His followers to gather for the Supper and nowhere mentions them jumping through ecclesiastical hoops. Pastors be very aware that when you deny a fellow believer the comfort and fellowship of the Table you are really telling our Lord that His guest list needs some refinement and you might just know better than Him who should be invited. Do you really want to place yourself in that position?