What does it call us to do?
If the only essential is faith in Christ, and unity means that we are intimately connected to all who profess this essential, then what that means in our modern world is that we have a responsibility to do more than just be happy with our own recognition of this truth. We must boldly and actively proclaim it to our brothers and sisters in Christ. And that is not necessarily easy.
Consider the historical examples of those who were married to people of different races or those who remarried after divorce. Consider the modern example of those who are hear without proper immigration status or who are gay. Is it enough for our little church to just quietly open its door? I think not.
For one, it was not fair to our brothers and sisters in Christ who were in mixed race couples or had been divorced. It is not fair to our brother and sisters who are here in violation of immigration law or who are gay. Our little progressive church has its own style of worship and Bible study that is pretty much its own. What about the gay man who prefers High Mass? What about the undocumented immigrant who enjoys a meditative worship? Or the divorced couple that likes singing "Old Rugged Cross"? Should then be condemned to singing from the Chalice hymnal and listening to intellectuals drone on about the Jesus Seminar or Spong's latest jab at literalists? Why? Because we are the only ones that will take them? That's unacceptable.
And for two, we owe it to our brothers and sisters in Christ who would turn them away. We are not at liberty to watch them sin against the body of Christ without alerting them to their misdeed. Will it be easy? No. At Sunday dinner it is best to avoid religion, sex and politics and these topics touch all three. But we have no choice. Indeed, they may disagree. They may think who you have sex with is in fact an essential. They are wrong, and we can't just be satisfied with being right. It is our obligation to our brothers and sisters with whom we are unified in the body of Christ to witness to them.
But not with violence or vitriolic rhetoric. In all things charity, after all.
Answer three: With charity, but with clarity, we are called to witness for equality.