Part of church accepting one is innocent (5)
I believe the answer is:
naive
'innocent' is the definition.
(similar in meaning)
'part of church accepting one' is the wordplay.
'part of church' becomes 'nave' (area of a church building).
'accepting' is an insertion indicator (inserted letters are accepted).
'one' becomes 'i' (Roman numeral).
'nave' placed around 'i' is 'NAIVE'.
'is' is the link.
(Other definitions for naive that I've seen before include "Simple-minded" , "Ingenuous, easily deceived" , "Credulous, unworldly" , "Showing lack of maturity or judgement" , "Inexperienced and guileless" .)