Jane Shaw, while speaking about the difference between Christian practice and Christian belief, identified that conversion as a result of belief statements rose to prominence during the Reformation. In contrast, the early Christian converts were often accepted as catachumens for a period of up to five years while they demonstrated their faith (e.g., taking care of widows, visiting the sick, feeding the poor, etc.). During this time they weren't allowed to participate fully in worship services.
If a pagan wished to become a Christian he was given some elementary instruction in the fundamental doctrines and practices of the Church. He had to show by his conduct that he was in earnest about the step he was about to take. So far, he was only in the stage of inquiry, and was not counted as a Christian at all. He was allowed to be present at the first part of the Mass, but he was dismissed immediately after the sermon.Catachumen, The Catholic Encyclopedia.
I have a natural hesitancy to wholly agree with this practice, since it's alien to me. It also seems to stand in the way of people coming straight to Christ, but I doubt whether the sincere catachumen was disuaded by this. They were clearly welcome into the community, but not completely. I hear echoes of Paul's admonishment about the communion meal in 1 Cor 11, but it seems like a misdirection.
Conversely, this practice indicates that a person isn't counted as a Christian until they have been instructed and have demonstrated the activity of the instruction. That's something of a sober warning to the post-Enlightenment Christian. Many of us became Christians on the basis of a statement of faith and have followed it with religious disciplines of bible reading, prayer and meeting together.
Widows and orphans, anyone? We have a lot to learn.
1. This passage seems to play with the "body of the lord" language between the bread and the Church. The "unworthy manner" appears to have more to do with failing to recognise the needs of fellow believers than it does with failing to recognise the bread as Christ's body.
2. "I turn to Christ, I repent of my sins, I renounce evil" in more traditional Churches and "I accept Jesus as my personal lord and saviour" in others are still just statements of doctrine and belief.