As he closes the letter, Paul isn’t messing around. He has discussed the insults against him, he has even taken on the personal of those insults. He has pleaded, he has reminded them of his connection to Christ. Now he tells them it’s time to clean up their act, cast off the old ways that they knew before they were in Christ. (This also seems like a pretty good indication of the difference between his message and that of his opponents.) But at the end he encourages joy and harmony. No problem, once we start acting like the people we’re supposed to be, right?