The cup of blessing which we bless, is it not the communion of the blood of Christ? The bread which we break, is it not the communion of the body of Christ? (17) For we, though many, are one bread and one body, for we all partake of that one bread.

The first letter to the Corinthians was written by the apostle Paul and in our verses today Paul is really addressing Christian corinthians and idolatry as in that pagan Culture they were used to attending idolatrous activities – eating meat previously offered in rites to idols; attending pagan feasts and celebrations. To make his point, Paul writes about the Lord’s Supper – a memorial of the death of Christ and the life of Christ given for men; basic doctrine vital to a celebration of the life of the Christian Church. Communion in the church is sharing; worshipping and participation in the Lord and in communion it begins with wine – the cup of blessing and symbol of the blood of Christ. And for communion we must be first in Christ that we may be united with each other; a spiritual union. Paul’s point here was that the Corinthians understand that Christians must even by external expression maintain that unity between Christ and us as we assemble to receive the symbol of that unity.
This reminder Is warning about eating in an idol temple and participating in pagan rituals. – the warning is there even though the Christians consider themselves strong, they were/are to know no one but the one true God and the possibility of getting caught up on idolatry was very real. PAul drew his lesson from the experience of Israel wandering in the wilderness. Self confidence can easily lead to a spiritual fall- failure was not inevitable but God provided the Lords supper and Christian fellowship to deal with cultic meals and temptations. PAul advised the Christians to FLEE idolatry. The cup of blessing was a common expression for the last cup drunk at any Jewish meals. PAul turns this around by saying we bless the cup because it symbolizes our sharing in Christ’s blood. Likewise the bread at a Christian feast is a symbol of our participation in Christ’s slain body.
Since it is one bread we the many are one body for Christians are all partakers of that one bread. It is one body by virtue of our joint participation.