Unpleasant task surrounding a line in hymn (7)
I believe the answer is:
chorale
'hymn' is the definition.
(chorale is a kind of hymn)
'unpleasant task surrounding a line' is the wordplay.
'unpleasant task' becomes 'chore' (I've seen this before).
'surrounding' means one lot of letters goes inside another.
'line' becomes 'l'.
'a'+'l'='al'
'chore' enclosing 'al' is 'CHORALE'.
'in' is the link.
(Other definitions for chorale that I've seen before include "vocal music" , "Stately hymn tune" , "Psalm or hymn tune" , "hymn setting" , "Lutheran hymn-tune" .)