Eucharist
1 Corinthians 10:16
The chalice of benediction, which we bless, is it not the communion of the blood of Christ? And the bread, which we break, is it not the partaking of the body of the Lord?
Context of the passage
Paul warns the Corinthians against idolatry by comparing pagan sacrificial meals to the Eucharistic communion of the Church.
Catholic reading
Paul's rhetorical question assumes real participation ('koinonia') in Christ's actual blood and body, not mere symbolism, which is why sharing pagan sacrifices would be spiritually incompatible.
Common objection
'Communion' could simply mean fellowship or remembrance among believers.
Response
The parallel Paul draws to pagan sacrifices (v.18-21), where eating truly unites one to the demon behind the idol, requires that Eucharistic communion likewise be a real participation in Christ, not a mere symbol.