"My neighbor is a Catholic and we were talking about communion one afternoon. She told me they believe the bread and wine actually become Christ's body and blood. Why do they believe that?"
The history of communion (also known as the Lord's Supper, the Eucharist, and Mass) is traced to the early church. Scripture tells us Jesus changed some of the traditional wording of the haggadah (the ritual stories and prayers) during the last Passover meal to suit his present circumstances. According to Paul in 1st Corinthians 11.23-24, Jesus took a piece of the matzoth bread, broke it, and gave it to those eating with him and said, "This is my body. Do this in remembrance of me." Then, after the meal was completed he took the wine and poured a glass for each and told them to drink it, that the wine was his blood.
The early church began to celebrate the Lord's Supper some years later, and most scholar's understanding of the earliest writings is the bread and the wine were considered to be just that, bread and wine symbols of Christ's crucifixion. However, in the next few centuries theologians began to study the words of institution and a gradual shift began. Within 300 years of the life of Christ the church had declared that the bread and the wine in the Lord's supper took on Christ-like characteristics when an appropriate ritual was recited in faith by one who was ordained (chosen and set apart) in the church.
What brought on the change? The understanding of the "words of institution," that is, Jesus' words, "This is my body" and "This is my blood." Theologians concluded when these words were recited in the name of Christ a change came over the "elements" (the bread and wine) such that they were no longer actually bread and wine, but actually the body and blood of Christ. This change, called transubstantiation, was effected by the work of God through the Holy Spirit.
This caused no little concern over the centuries. For many years the Eucharist was regarded as so holy and mystical only priests were allowed to partake. Later, the bread was distributed to those in worship (mass), but the wine was withheld. Even today, partaking of the wine in the Roman Catholic Church is considered to be an option by some.
The Reformation (the Protestant movement) in the 1500s brought a new crop of theologians to the forefront of scholarship. They concluded the elements did not actually change through the ritual. Instead, depending on which theologian you read, the elements either invoked the presence of Christ within the person (consubstantiation), or else evoked the memory of Christ's sacrifice.
Today churches worldwide celebrate communion regularly. Some churches, including the Roman Catholic Church offer the Mass several times each week. Other churches offer communion only quarterly, some even less. But in most churches the celebration of communion is a special event, and on October 6th Christian churches throughout the world will celebrate World Communion Sunday.
Communion is one of the holiest sacraments in the church today, and as a sacrament it contains a great measure of mystery. No one church, no one individual, has a corner on the truth of this age-old rite. Instead, the sacrament of communion is like a multi-faceted jewel: everyone sees the sparkle from different angles and marvels at its beauty. For some communion is a literal sharing in the suffering and death of Christ; for others communion is a source of strength and comfort; and for still others it's a reminder of the high cost of commitment. Many facets, many truths, many mysteries. May the Eucharist always capture within us a sense of awe regardless of what we may believe.