His rector ordered one will perform in church (9)
I believe the answer is:
chorister
'one will perform in church' is the definition.
'his rector ordered' is the wordplay.
'ordered' indicates anagramming the letters.
'his'+'rector'='hisrector'
'hisrector' is an anagram of 'CHORISTER'.
(Other definitions for chorister that I've seen before include "Boy in church" , "Church, cathedral singer" , "Choirboy or girl" , "Boy singer" , "Choir member" .)