Sermon topic (3)
I believe the answer is:
'sermon topic' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sin that I've seen before include "'Transgression, mortal or venial (3)'" , "Immorality" , "Transgression of moral law" , "Immoral action" , "Wrongdoing" .)