Vital element of German city church (7)
I believe the answer is:
essence
'vital element' is the definition.
(I've seen this before)
'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 heart of" , "Extract; intrinsic nature" , "Perfume or concentrated extract" , "Distinctive inner nature of person or thing" , "Flavour, spirit" .)