Catholic sect I once infiltrated for operation (1-7)

'operation' is the definition.
(I know that C-section is a type of operation)

'catholic sect i once infiltrated for' is the wordplay.
I cannot really understand how this works, but
'catholic' could be 'c' (abbreviation as in RC for Roman Catholic) and 'c' is located in the answer.
'i' is found in the answer.
'for' could be 'to' (eg both can mean 'in the opinion of') and 'to' is found in the leftover letters.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?