Maybe one pardoning sins to which man’s been prone? (8)
I believe the answer is:
chaplain
'maybe one pardoning sins' is the definition.
'man's been prone?' is the wordplay.
'man' becomes 'chap' (I've seen this in other clues).
'been prone?' becomes 'lain'.
'chap'+'lain'='CHAPLAIN'
'to which' acts as a link.
(Other definitions for chaplain that I've seen before include "'Member of the clergy, in a hospital, say (8)'" , "Clergyman attached to military unit" , "Army padre" , "Clergyman attached to an institution, such as the army" , "Religious minister assigned to an organisation" .)