Having purpose gives us new heart (3)
I believe the answer is:
use
'having purpose' is the definition.
I can't judge whether this definition defines the answer.
'us new heart' is the wordplay.
'heart' means to look at the middle letters.
The centre of 'new' is 'e'.
'us'+'e'='USE'
'gives' is the link.
Can you help me to learn more?
(Other definitions for use that I've seen before include "consume; exploit" , "Put into service, do something with" , "Exploit unfairly" , "Function, purpose" , "Practise" .)