Particular church rings Stepney’s boundaries (6)
I believe the answer is:
choosy
'particular' is the definition.
(synonyms)
'church rings stepney's boundaries' is the wordplay.
'church' becomes 'ch' (common abbreviation).
'rings' becomes 'oo' (two O's - O resembles a ring).
'boundaries' suggests removing the centre (only the edge or boundary letters remain).
'stepney' with its middle removed is 'sy'.
'ch'+'oo'+'sy'='CHOOSY'
(Other definitions for choosy that I've seen before include "Fastidious, finicky" , "Fastidious (colloq.)" , "Fussy, particular" , "Selective" , "Discriminating" .)