With eschewing personal benefit, no energy for task (4)
I believe the answer is:
onus
'for task' is the definition.
(I've seen this in another clue)
'with eschewing personal benefit no energy' is the wordplay.
'with' is an insertion indicator.
'eschewing' suggests deleting specific letters.
'personal' becomes 'one's' (belonging to oneself).
'benefit' becomes 'use' (I've seen this before).
'energy' becomes 'ons' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'use'+'no'='useno'
'useno' with 'ones' taken out is 'u'.
'u' inserted within 'ons' is 'ONUS'.
Can you help me to learn more?
(Other definitions for onus that I've seen before include "Liability" , "Obligation - charge" , "'Responsibility, task or burden (4)'" , "Weight of responsibility" , "'Burden, of proof (4)'" .)