I can imagine a world where everyone was accepted at the Lord's table. No matter who you were, no matter what you had done, or what you believed, you were able to sit down and share in the Lord's supper.
One person would say to the next, "Isn't it great that we can share this together in unity, and yet retain our individuality?" The other person would say, "Yes, it's great! But who is this Jesus character, and why does he walk around here acting as if he is God?"
"What do you mean?" questions the first, with a strange look on his face. "Jesus IS God."
"What?! Are you off your rocker? Jesus is not God..."
"Are you trying to tell me what to believe? That is against the spirit of this table, that everyone is accepted no matter what they believe. I believe that Jesus is not God, and you can't tell me that I am wrong", retorts the second, indignantly.
"Calm down now, yes I know that you are allowed to believe what you want. But please, brother, at least try to be loving."
"Who says that I have to be loving? Are you trying to force yet another restriction on me?"
"Well, God IS love, and Jesus commands us to love our neighbor."
"There you go, blathering on about Jesus again. Jesus can't tell me what to do, only God can."
"Well, if Jesus is not God, then why are you interested in sharing His table?"
"I want to be in community with other believers, and the table is the sign of that unity. Don't you know what community means? Community is "common unity"..."
"It is clear to me, brother, that there is no unity here, since you don't believe that Jesus is God, and I do".
The second person says then to the first, "Then it sounds like you should high-tail it out of here."
Around such a table, the constant question in everyone's minds would be about why we are sharing a sign of unity while we are not united. No one would have any right to state that what they believed is correct. The resulting conversation, rather than being about God, would have to be about anything BUT God - small talk, the weather, even politics would be talked about before someone talked about God.
God is the ultimate dividing force, because He is Truth, and because of the fallen nature of man. Man, almost from the beginning, was tempted to believe that he could be like God: to determine good and evil, right and wrong, truth from falsity, for himself. Certainly fallen man is not naturally inclined to submit to another human being, whose "opinion" they certainly don't regard as better than their own, but rather (more than likely) "inferior".
Belief will always separate us until we submit in humility to God; only then can we sit around the Lord's table, love the Truth and good gifts that God has bestowed upon us, ponder how good God is for giving us those gifts, and ponder the higher mysteries without needing to argue about them.
In heaven, those who make it there will not formulate their own opinions about God, but will submit to God who is Truth and will partake in the Lord's table with one mind, the mind of God.
That is why I believe that closed communion, with submission to divinely revealed truths, rather than opinions that a person has determined for himself, most closely reflects the heavenly reality of sitting around the Lord's table.
God did not leave us orphans, forced to take a book and interpret it for ourselves. He gave us the Catholic Church so that we can enjoy this unity, and so that, rather than quarreling between ourselves, we could know that we had the truth in the first place, and thus free our minds to travel deeper into the reality of God, and through that contemplation of God, come to know more fully what God's love is, and to then love God in return. Our God, who is truth, does not settle for superficial union, but insists on complete union, sharing in the divine nature, a union akin unto the unity that is God Himself, a union in all things, in mind, in love, in spirit.