If I may bring up a verse in Acts 18:9-10 it seems like Corinth was a city where wickedness prevailed and Paul had to be reassured by Christ not to be afraid. Now these were the ones now saved and trusting in Christ. Some of the sins of the past did not immediately just fall off.
However now Paul writes a different kind of letter still a little correction and instructive doctrine. He also has to vindicate himself as an apostle to some at the end of this letter. Some parts are very precious to me as to our resurrection and eternal life.