The Lord's Supper
To their enemies, the early Christians were thought to be cannibals, based on a misunderstanding of the central focus of those early Christian meetings, where bread and wine were shared as Christ's "flesh" and "blood."
A Shared Meal
At first, the Eucharist consisted of a common meal, where the bread and the wine were shared as a vivid reminder of the death and resurrection of Jesus, and of the shared role of all Christians, who had died to sin in the death of Jesus, resurrected to a new life in Christ.
Some of the Mennonite churches still celebrate the Lord's Supper as a common meal, but most of the Western churches gradually began to put more emphasis on celebrating the Eucharist or mass, and on the power that was believed to spring from this reenactment of Christ's sacrifice of Himself upon the cross.
In time, the Popes came to threaten obstinate rulers with exclusion from the Eucharist, which was thought to be a powerful sanction, carrying the threat of exclusion from heaven. Priests used similar tactics when dealing with wayward flocks.
Eventually, people began to attach a magical significance to the bread and the wine, with ordinary Christians barred, as unfit to drink the wine.
It wasn't until 1215 that the Church began teaching what became the doctrine of transubstantiation. The 4th Lateran Council proclaimed in that year that:
The Body and Blood are truly contained in the Sacrament ... under the appearance of bread and wine, after the bread has been changed into the Body, and the wine into the Blood, through the power of God.
16th Century reformers would later reject the Catholic doctrine of transubstantiation.
Martin Luther demanded that all believers should be offered both bread and wine, and declared that the bread and wine benefited those who accepted them in faith, but that they did not change into the actual body and blood of Christ. He believed that the taking of the bread and the wine benefited those believers who accepted them in faith, but that the process was not mechanical.