On Closed Communion

The following is my response to one of my catechumens to the question of why the Orthodox Church practices a closed communion:

Basically, Communion creates and defines our community, our being one with one another in Christ—i.e. eating of the one bread and of the one cup. Historically, some people/groups separated themselves from the communion of the Church through heresies or immorality or aligning themselves with a heretical bishop. Therefore, they are not in communion, not part of the one Church—at least as far as we can identify the Church as a concrete divine/human institution (not to be confused with “all who will be saved in heaven,” which only God knows). Anyone can return to communion with the one Church through repentance and Chrismation (or whatever specific rite the bishop decides). We do not have open communion because we don’t want to say people are part of the Church who are not part of the Church—or at least whom we can’t identify as part of the Church. This would be dangerous for them (eating and drinking condemnation to themselves) and dangerous for us (through Communion we become one with one another.