German city church in vital part (7)
I believe the answer is:
essence
'vital part' is the definition.
'german city church' is the wordplay.
'german city' becomes 'essen' (city in Germany).
'church' becomes 'CE' (abbreviation for Church of England).
'essen'+'ce'='ESSENCE'
'in' acts as a link.
(Other definitions for essence that I've seen before include "Plant extract or concentrate" , "Crux" , "Scent; core" , "The most distinctive element" , "Nice fuel" .)