What is the one bread in I Corinthians 10:17? Not everyone takes of one bread. One person told me that it was one kind of bread; that is, if I understand correctly, unleavened bread.
"Is not the cup of blessing which we bless a sharing in the blood of Christ? Is not the bread which we break a sharing in the body of Christ? Since there is one bread, we who are many are one body; for we all partake of the one bread" (I Corinthians 10:16-17).
The emphasis in this passage is that partaking of the Lord's Supper is a sharing between many members. It harkens back to the covenant meals under the Old Testament where those who entered a covenant shared a meal together to show they were at peace with each other (Genesis 31:51-54; Exodus 24:9-11).
The one cup was divided by the Lord and shared with his disciples (Luke 22:17-20). A loaf was divided and shared as well. The fruit of the vine in the cup symbolizes the shed blood of Christ and the bread his broken body. Just as Christ was one person, we who share in the Lord's Supper are stating we are the one body of Christ, the church (Colossians 1:24).
A local congregation is not the whole of the body of Christ. Therefore, the emphasis in this passage is the fact that all Christians participate in the observance each week (Acts 20:7) and, thus, show they are a part of the universal church, the one body. It isn't the number of containers or the number of loafs required, it is the fact that we are doing it together as the body of Christ that is the concern in this passage.
Other passages, such as I Corinthians 11:18,20, tells us the local church is to meet together to partake of the Lord's Supper and that partaking is to be done together. "So then, my brethren, when you come together to eat, wait for one another" (I Corinthians 11:33). They are scolded for not eating the Lord's Supper together, "for in your eating each one takes his own supper first; and one is hungry and another is drunk" (I Corinthians 11:21).
Therefore, I Corinthians 10:16-17 gives emphasis to the unity of the whole church throughout the world through the Lord's Supper, and I Corinthians 11:17-34 gives emphasis to the unity of the local congregation in their participation in the Lord's Supper.