Some years ago I had a brief exchange of emails with an Anglican clergyman who lives a little distance away. It's an exchange I will always remember. His parish was, I think, part of the American group that had a pastoral relationship with some of the Anglicans in Africa. I don't really understand all the connections, and I don't know who's in communion with whom, but he came across as a very nice man who plainly loves Christ. He was writing to express his interest in talking with me, so I let him know I'd be delighted to see him, and we suggested some possible dates and times.
One of my suggestions was a time right after one of the weekday Masses. "In fact," I wrote, "perhaps you'd like to come to the Mass, and we can meet right afterwards." That sounded like a great idea to him, and I thought we were set.
Then I got another email. "Am I ok for Holy Communion?" I knew what he was asking, and I wondered why he would even ask. "Sadly, no," I wrote back, "I'm a priest under orders, as I know you understand, and I wouldn't be able to administer Holy Communion to you."
Here's what he wrote back: "This is one of the things that stands in the way of real unity - the RCC treats other Christians as though they aren’t really Christians - denying them the Body and the Blood. This is especially problematic in light of the fact that you and I do nearly the same service, and our ordinations share many of the same apostolic roots, along with a common apostolic succession. That’s gotta hurt the cause of Christ in a world that desperately, desperately needs Him."
It was probably my fault because had I invited him to attend the Mass. Maybe that's why he took it as more than just an invitation to be there, although his response made it obvious that he knew the answer before he asked the question. His blanket statement that Catholics treat others as though they're not really Christians is based solely upon the fact that we don't have a "come one, come all" policy at the Communion rail. He knows the Church doesn't deny that he's a Christian. In fact, the Church teaches explicitly that all those who are validly baptised belong to Christ. And then there's the subtle slap, that I'm hurting the "cause of Christ" because I won't allow him to receive Holy Communion. The problem is, most protestants view Holy Communion as a means of achieving the unity Christ desires; whereas the Catholic understanding is that it's sign of the unity of faith we're supposed to have already. So how can we best understand the vast difference between those two understandings?
Maybe St. Paul can help. In his epistle to the Ephesians, he holds up the relationship Christ has with the Church as being an image of the marriage relationship. That image provides a very helpful picture to us, when it comes to Holy Communion.
We've all known young couples who decide that they're going to live together, and have a sexual relationship, because they think it will somehow bring them closer together, and help them find out if they should get married. In effect, they want to pretend they're married, in the hope that it'll lead to the real thing. Of course, it doesn't. It cheapens God's gift of sexuality. And even if they do eventually marry, you can be sure that the anniversary they keep isn't going to be the anniversary of the first time they had sexual intercourse.
Having a sexual relationship outside of marriage gives a fake impression of a sacred union. It's unsatisfying, and eventually one or both of the partners starts to feel used. At some point there comes a desire either to end it, or else to make it permanent. It's only when a man and a woman have bound themselves together before God by "pledging their troth each to the other" - by making solemn vows to one another before God - it's only then that their sexual relationship can be what God intends it to be.
Keep that image in mind - the image of a man and woman bound by vows made before God. Now think about trying to achieve Christian unity by having everybody receive Holy Communion, no matter what they believe. It's like sex before marriage. It's only an illusion of unity.