Bits of hymns in church old vicar finally employs (8)
I believe the answer is:
choruses
'bits of hymns' is the definition.
(hymns have choruses)
'church old vicar finally employs' is the wordplay.
'church' becomes 'ch' (abbreviation on maps etc).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'finally' says to take the final letters.
'employs' becomes 'uses' ('use' can be a synonym of 'employ').
The final letter of 'vicar' is 'r'.
'ch'+'o'+'r'+'uses'='CHORUSES'
'in' is the link.
(Other definitions for choruses that I've seen before include "Parts of songs repeated after each verse" , "Parts of songs where soloist is joined by group of singers" , "Groups of singers supporting soloists" , "Choral numbers" , "Groups of singers or song refrains" .)