It makes creature be a saint! (5)
I believe the answer is:
beast
'it' is the definition.
The definition suggests a singular noun which matches the answer.
'makes creature be a saint' is the wordplay.
'makes creature' becomes 'be' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'saint' becomes 'st' (abbreviation).
'be'+'a'+'st'='BEAST'
Can you help me to learn more?
(Other definitions for beast that I've seen before include "Wild animal" , "Animal, creature" , "Pig" , "beef?" , "Animal; cruel person" .)