See core ideas changing about Church (11)
I believe the answer is:
archdiocese
'see' is the definition.
(thesaurus)
'core ideas changing about church' is the wordplay.
'changing' indicates an anagram.
'about' indicates putting letters inside.
'church' becomes 'ch' (common abbreviation).
'core'+'ideas'='coreideas'
'coreideas' anagrammed gives 'ardiocese'.
'ardiocese' placed around 'ch' is 'ARCHDIOCESE'.
(Other definitions for archdiocese that I've seen before include "Important church area" , "eg York" , "York, say" , "York, for example" .)