In Chapter 5 of 1 Corinthian, St. Paul begins to address the specific issues that he has heard about that have been dividing the Church in Corinth. This chapter gave us great discussion on excommunication, mercy, forgiveness, and the expectation that Christians SHOULD judge those INSIDE the Church, but NOT those OUTSIDE.
http://stjohnjackson.org/scripture_study/1_Corinthians_Pg_13_14.pdf