Ritual and Sacrament
The importance of Holy Communion is that it is a sacramental act. Sacraments are set above and apart other kinds of ritual activity.
The Elements of Holy Communion
Holy Communion is modeled after The Last Supper of Jesus with his disciples in which he offered each a piece of bread from a broken loaf and a drink of wine. The broken loaf represents his injured flesh brought on by scourging and crucifixion. The wine is a symbol of the blood that Jesus shed.
Transubstantiation
One way that the Christian Church understands Holy Communion is in terms of transubstantiation. When the priest consecrates the communion elements, Catholics believe that the substance of the bread and wine itself is transformed literally into the body and blood of Jesus.
Consubstantiation
Protestant churches understand Holy Communion in terms of consubstantiation or that the elements contain the essential, redemptive qualities of the suffering, death and resurrection of Jesus.
Open and Closed
Some Christian communities limit communion participation only to members (sometimes non-members who meet a particular theological criterium) and others open communion to all who wish to partake.
Frequency
At The Last Supper, Jesus admonished the disciples to partake of the bread and wine as often as they wished.