Lack cake decorating skills when receiving large number of churchgoers (8)
I believe the answer is:
canticle
'number of churchgoers' is the definition.
(number meaning song)
'lack cake decorating skills when receiving large' is the wordplay.
'lack cake decorating skills' becomes 'Can't ice'.
'when receiving' is an insertion indicator.
'large' becomes 'l'.
'cantice' enclosing 'l' is 'CANTICLE'.
(Other definitions for canticle that I've seen before include "Short hymn" , "A religious song" , "is heard in church" , "Liturgical song" , "Church hymn or chant" .)