Man needing a change of heart and belief (3)
I believe the answer is:
ism
'belief' is the definition.
(the -ism suffix in the names of belief systems)
'man needing a change of heart' is the wordplay.
'man' becomes 'm'.
'needing' says to put letters next to each other.
'a change of heart' becomes 'is' (I can't justify this - if you can you should believe this answer much more).
'm' after 'is' is 'ISM'.
'and' is the link.
(Other definitions for ism that I've seen before include "Doctrine, philosophy" , "Suffix denoting doctrine or practice" , "Suffix denoting doctrine or practise" , "Ideological movement" , "Any branch of philosophy" .)