The sermon opens with the Apostles' Creed, set beside its older wording. Two phrases are explained. "He descended to the dead" speaks of Christ entering the state of death, which is the sense of Hades, and not the place of final punishment. And "the holy catholic church" means the universal church: every true believer in every time and place, set apart unto God in Christ, the body in which the communion of saints and the forgiveness of sins are a present reality.
From there Paul's letter shows how badly one congregation could forget it. Corinth had factions, boasting, immorality, lawsuits and disorder in worship, and at the Lord's table some went hungry while others were drunk. Paul answers by repeating what he received from the Lord: the bread is Christ's body given for us, and the cup is the new covenant in His blood. To eat and drink worthily is to recognize and celebrate the atonement, to examine ourselves, and to wait for one another. When the Lord judges His people, He is disciplining them so that they will not be condemned along with the world.