Naughty bits apt to make one religious (7)
I believe the answer is:
baptist
'one religious' is the definition.
(a religious person)
'naughty bits apt' is the wordplay.
'naughty' is an anagram indicator.
'bits'+'apt'='bitsapt'
'bitsapt' anagrammed gives 'BAPTIST'.
'to make' is the link.
(Other definitions for baptist that I've seen before include "Protestant church member" , "John, for example" , "Variety of Protestant" , "Type of Christian" , "Variety of Christian" .)