'Preach to choir!' minister to roar, ultimately in shock (6)
I believe the answer is:
horror
'shock' is the definition.
(I have seen 'Intense shock ' mean 'horror' so perhaps 'shock' could also mean 'horror')
'preach to choir minister to roar ultimately' is the wordplay.
'ultimately' suggests the final letters.
The last letters of 'preach to choir minister to roar' are 'HORROR'.
'in' is the link.
(Other definitions for horror that I've seen before include "Intense fear/disgust" , "Intense and profound fear" , "Great dismay" , "Extreme aversion" , "Intense repugnance" .)