Evangelists start stirring humanist's passion (10)
I believe the answer is:
enthusiasm
'passion' is the definition.
(thesaurus)
'evangelists start stirring humanist's' is the wordplay.
'start' suggests taking the first letters.
'stirring' is an anagram indicator.
The initial letter of 'evangelists' is 'e'.
'humanists' anagrammed gives 'nthusiasm'.
'e'+'nthusiasm'='ENTHUSIASM'
(Other definitions for enthusiasm that I've seen before include "Avidity" , "Gusto; fervour" , "spirit?" , "Intense and lively interest" , "Ardour" .)