Gathering at a church service in German (8)
I believe the answer is:
amassing
'gathering' is the definition.
('amass' can be a synonym of 'gather')
'a church service in german' is the wordplay.
'church service' becomes 'mass' (I've seen this before).
'german' becomes 'g' (abbreviation).
'a'+'mass'+'in'+'g'='AMASSING'
'at' is the link.
(Other definitions for amassing that I've seen before include "gathering" , "Making a collection of" , "Accumulating a large amount" , "Putting together" , "Building up (a stock)" .)