en_tn_condensed/2co/01/01.md

Paul ... to the church of God that is in Corinth

"I, Paul ... wrote this letter to you, the church of God that is in Corinth" In this book, the word "I" refers to Paul. Also, the word "you" is almost always plural and refers to the believers in Corinth. There are two exceptions to this: 6:2 and 12:9.

Timothy our brother

This indicates that both Paul and the Corinthians knew Timothy and considered him to be their spiritual brother.

Achaia

This is the name of a Roman province in the southern part of modern-day Greece.