Join because church welcomes alcoholic drink (8)
I believe the answer is:
coalesce
'join' is the definition.
(I've seen this before)
'because church welcomes alcoholic drink' is the wordplay.
'because' becomes 'cos' (I've seen this in other clues).
'church' becomes 'CE' (abbreviation for Church of England).
'welcomes' means one lot of letters goes inside another (in sense of 'invites in').
'alcoholic drink' becomes 'ale' (type of beer).
'cos'+'ce'='cosce'
'cosce' enclosing 'ale' is 'COALESCE'.
(Other definitions for coalesce that I've seen before include "Join into one mass" , "Merge into one" , "Come together in one mass" , "Unite" , "'Fuse, combine (8)'" .)