Eucharist—usually called communion—is the essential Christian sacrament, the centerpiece of Christian worship. When a sacrament persists for millennia as a defining ritual, it’s telling us something about how earliest followers understood their journey. It can also tell us what we’ve forgotten about ours.

Eucharist means thanksgiving…because Jesus gave thanks over bread and wine at that last supper…because we should gratefully remember Jesus’ sacrifice on the cross, the means by which sins are f...