Fundamental nature seen in German City Church (7)
I believe the answer is:
essence
'fundamental nature' 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'
'seen in' acts as a link.
(Other definitions for essence that I've seen before include "The heart of" , "Soul" , "Crux" , "Perfume or concentrated extract" , "Perfume or concentrate" .)