Fail to double congregation (4)
I believe the answer is:
fold
I believe this is a triple definition!
'fail' is the first definition.
(as in a business folding)
'to double' is the second definition.
(thesaurus)
'congregation' is the third definition.
(as in welcoming someone into 'the fold')
(Other definitions for fold that I've seen before include "Church following" , "Cease trading" , "Bend over; pen" , "Crease" , "Collapse; bend in half" .)