Friend leading Mass including second devotional song (5)
I believe the answer is:
psalm
'devotional song' is the definition.
(I've seen this before)
'friend leading mass including second' is the wordplay.
'friend' becomes 'pal' (pal is a kind of friend**).
'leading' indicates taking the first letters.
'including' indicates putting letters inside.
'second' becomes 's' (common abbreviation).
The initial letter of 'mass' is 'm'.
'pal'+'m'='palm'
'palm' placed around 's' is 'PSALM'.
(Other definitions for psalm that I've seen before include "A song which praises" , "Sacred song from Old Testament" , "Sacred song of praise" , "Jewish hymn" , "What's heard in church" .)