Protestant bishop, suitable at first (7)
I believe the answer is:
baptist
'protestant' is the definition.
(Baptist is an example)
'bishop suitable at first' is the wordplay.
'bishop' becomes 'B' (chess abbreviation).
'suitable' becomes 'apt' (apt means appropriate or fitting).
'at' means one lot of letters go next to another.
'first' becomes 'ist' (ist resembles 1st).
'b'+'apt'+'ist'='BAPTIST'
(Other definitions for baptist that I've seen before include "Protestant church member" , "John, for example" , "Variety of Christian" , "Type of Christian" , "Protestant advocating total immersion at a christening" .)