The Feast of the Most Holy Body and Blood of Christ (Corpus Christi) celebrates the ancient tradition concerning the Sacrament of Eucharist. From the earliest times in the church, and right within the Gospels, we see this focal point of christian celebration in the writings and practice of early christians as well as in the very words of Christ at the last supper where He states concerning the bread and wine that: “This is my body; This is my blood”.
In the Catholic Church there is a term called Transubstantiation which defines how we understand the Real Presence. It states that during the consecration at Mass a change occurs where the “Accidents” of bread and wine become the “body, blood, soul and divinity” of Christ substantially. The physical appearance of bread and wine remain. The concepts of substance and accident were not inventions of the church, but come from philosophy. The basic idea is that a thing can truly be something other than what it appears to be. This is a concept not confined to the Eucharist alone. Baptism, Marriage, Orders, and the other sacraments also hold to a hidden and real grace that is bound to the physical but not necessarily seen. For instance Marriage is not a matter of a mere documented forensic declaration; it is a substantial reality that the man and woman have become one flesh. Not seen in appearance or the physical but understood in a “spiritual” way. Other examples can be found in scientific terms like physical change. For instance the substance of h2o can make up ice, water and steam. The outside appearance doesn’t change the substance within.
The Feast of Corpus Christi has some interesting traditions which are still practiced. One of these would be the procession of the Eucharist in a Monstrance. A Monstrance is a vessel, which the Host (Eucharist) can be placed into for adoration. The word comes from the Latin monstrare which means “to show” (think demonstrate) and during the year many parishes have times set for Eucharistic Adoration. Worshippers can come and sit before the Sacrament, to pray , contemplate, and meditate. During Corpus Christi it was common to form a procession that would carry the Host through the town in a monstrance, and while it is not common, this practice is still observed by some today.
In the last several centuries the belief in the real presence and especially the catholic definition of transubstantiation have been challenged. Early reformers like Luther still held a similar concept which was termed consubstantiation, and the feast of Corpus Christi was retained for a time. In many of the modern sects the belief is completely rejected. In a way which I find ironic, the belief that the bread and wine become the Body and Blood of Christ has been “transubstantiated” into a belief that the bread and wine have become crackers and grape juice.
“This food we call the Eucharist, of which no one is allowed to partake except one who believes that the things we teach are true, and has received the washing for forgiveness of sins and for rebirth, and who lives as Christ handed down to us. For we do not receive these things as common bread or common drink; but as Jesus Christ our Savior being incarnate by God’s Word took flesh and blood for our salvation, so also we have been taught that the food consecrated by the Word of prayer which comes from him, from which our flesh and blood are nourished by transformation, is the flesh and blood of that incarnate Jesus.”
Justin Martyr: “First Apology”, Ch. 66, inter A.D. 148-155.