Very little in Catholic teaching initially was read during troubles (4,3)
I believe the answer is:
riot act
'was read during troubles' is the definition.
(act historically read out during disturbances)
'very little in catholic teaching initially' is the wordplay.
'very little' becomes 'iota' (an iota is a tiny amount).
'in' means one lot of letters goes inside another.
'catholic' becomes 'rc' (Roman Catholic).
'initially' suggests taking the first letters.
The initial letter of 'teaching' is 't'.
'iota' put inside 'rc' is 'riotac'.
'riotac'+'t'='RIOT ACT'
(Other definitions for riot act that I've seen before include "used to deal with unrest" , "Citator may read this as stern rebuke" , "something read to little devils?" , "Citator of law concerning public affray" , "It's read in the face of disturbances" .)