Chap joins new church for this reason (5)
I believe the answer is:
hence
'for this reason' is the definition.
(I've seen this in another clue)
'chap joins new church' is the wordplay.
'chap' becomes 'he' ().
'joins' is a charade indicator (letters next to each other).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'church' becomes 'CE' (abbreviation for Church of England).
'he'+'n'+'ce'='HENCE'
(Other definitions for hence that I've seen before include "Therefore, consequently" , "It follows from that fact" , "Thus" , "As a result" , "In the future; begone!" .)