The Eucharist (Greek eucharistia, thanksgiving), also called the Mass, the Divine Liturgy, Holy Communion or the Lord's Supper, is the ritual re-enactment of the Last Supper, in which bread and wine are consecrated and shared. Its warrant is the command reported in the Synoptic Gospels and, earliest of all, in Paul's first letter to the Corinthians from around the middle of the first century: Do this in remembrance of me. From the second century it stands at the center of Christian worship, and the shape Justin Martyr describes in his First Apology around the middle of that century, readings, common prayer, the offering of bread and wine, a great thanksgiving, and distribution, is recognizably the shape still followed.
How often ordinary believers actually received communion, however, changed dramatically over the centuries in a way the rite's continuous outward shape can obscure. Early Christian practice generally involved frequent, often weekly, communion for the whole congregation, but by the high medieval period lay reception had become rare enough, amid growing awe around the consecrated elements and a corresponding rise in the practice of merely watching the priest communicate, that the Fourth Lateran Council in 1215, the same council that defined transubstantiation, found it necessary to mandate a minimum: every believer of age was required to confess and receive communion at least once a year, around Easter, a rule remembered as the Easter duty and one that only makes sense against a backdrop of declining lay participation in the rite it was meant to safeguard.