Idiot guards Catholic church entrance (6)
I believe the answer is:
access
'entrance' is the definition.
(thesaurus)
'idiot guards catholic church' is the wordplay.
'idiot' becomes 'ass' (I've seen this before**).
'guards' is an insertion indicator.
'catholic' becomes 'c' (abbreviation as in RC for Roman Catholic).
'church' becomes 'ce' (abbreviation for Church of England).
'c'+'ce'='cce'
'ass' enclosing 'cce' is 'ACCESS'.
(Other definitions for access that I've seen before include "Means or way of gaining entry" , "Credit" , "The right to use something or see someone" , "Admission" , "OK to go in" .)