The men, even the ones who are thought to possible cause trouble, usually go to church and don’t drink on Sundays. What makes this a special occasion?

Church is a time when everything stops and the people get dressed up and spend time with God and loved ones. Regardless of religion, the people all go to church and they try to live better lives on that day.

This particular Sunday is a special occassion because Tom Robinson's trial is just around the corner. The men of Maycomb are concerned about Tom's presence in the local jail and possible trouble. Atticus doesn't think there will be trouble, but the rest of the men believe there will be problems. The special occassion in the trial.