Quietly correcting His holy work involved discipline (10)
I believe the answer is:
'discipline' is the definition.
(I know that philosophy is a type of arts)
'quietly correcting his holy work involved' is the wordplay.
I cannot really see how this works, but
'quietly' could be 'p' (p for piano and quiet) and 'p' is found within the answer.
'work' could be 'op' (abbreviation for opus) and 'op' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for philosophy that I've seen before include "Outlook" , "Study of truth - attitude to life" , "Study of being, meaning etc" , "Calmness of temper" , "behavioural attitude" .)