In song, it’s for ordinary people (5)
I believe the answer is:
laity
'ordinary people' is the definition.
(I've seen this before)
'in song it's' is the wordplay.
'in' is an insertion indicator.
'song' becomes 'lay' (lay is a kind of song).
'it's' becomes 'it' (I've seen this in other clues).
'lay' going around 'it' is 'LAITY'.
'for' is the link.
(Other definitions for laity that I've seen before include "They're not the clergy" , "People not ordained" , "Laymen" , "Non-experts" , "Unordained people" .)