Body of church unchanged welcoming Son (7)
I believe the answer is:
chassis
'body' is the definition.
(I know that chassis is a type of body)
'church unchanged welcoming son' is the wordplay.
'church' becomes 'ch' (common abbreviation).
'unchanged' becomes 'as is' (as things currently are).
'welcoming' is an insertion indicator (in sense of 'inviting in').
'son' becomes 's' (genealogical abbreviation for son).
'asis' enclosing 's' is 'assis'.
'ch'+'assis'='CHASSIS'
'of' acts as a link.
(Other definitions for chassis that I've seen before include "basic structure" , "Vehicle structure" , "Body frame" , "Car framework" , "Vehicle's structure" .)