Song in church provided by a new boy (7)
I believe the answer is:
chanson
'song' is the definition.
(I have seen 'French song' mean 'chanson' so perhaps 'song' could also mean 'chanson')
'church provided by a new boy' is the wordplay.
'church' becomes 'ch' (common abbreviation).
'provided by' means one lot of letters go next to another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'boy' becomes 'son' (synonyms).
'ch'+'a'+'n'+'son'='CHANSON'
'in' is the link.
(Other definitions for chanson that I've seen before include "A number" , "(French) song" , "song for Piaf?" .)