Choosing the best extract from novel — it is marvellous (7)
I believe the answer is:
elitism
'choosing the best' is the definition.
'extract from novel it is marvellous' is the wordplay.
'extract from' indicates a hidden word (I've seen this in other clues).
'ELITISM' can be found hidden inside 'novel it is marvellous'.
(Other definitions for elitism that I've seen before include "that characterises some snobs?" , "goverment by chosen group" , "Belief in the best" , "Practice of favouring the best people" , "going for the best" .)