Vital part of German city church (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'
'of' acts as a link.
(Other definitions for essence that I've seen before include "The quality that makes something what it is" , "Perfume or concentrated extract" , "Scent; core" , "Flavour, spirit" , "Perfume; core" .)