A very quiet organ on a new church show (10)
I believe the answer is:
appearance
'show' is the definition.
(I know that show can be written as appearance)
'a very quiet organ on a new church' is the wordplay.
'very quiet' becomes 'pp' (musical abbreviation for pianissimo).
'organ' becomes 'ear' (the ear is an organ).
'on' means one lot of letters go next to another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'church' becomes 'CE' (Church of England).
'a'+'pp'+'ear'+'a'+'n'+'ce'='APPEARANCE'
(Other definitions for appearance that I've seen before include "show" , "Advent" , "air" , "Someone present has put one in" , "Semblance" .)