The key to unity is not for us all to agree on everything. Yes, we do agree on Jesus being our Lord and that he died for our sins and was raised from the dead. There are some other central truths that we all believe and that help hold us together as well. But once all that is settled, the next step toward unity is not to systematically discuss and decide the correct view on every possible issue. Rather, in 1 Corinthians 1-4, Paul addresses the division in the Corinthian church and shows us that the key to unity is an attitude of humility that grows out of the cross of Christ.
