Poetic incitement to assemble given in speech (6)
I believe the answer is:
orally
'in speech' is the definition.
(oral means relating to speech)
'poetic incitement to assemble given' is the wordplay.
'poetic incitement' becomes 'o' (I am not sure about this - if you are sure you should believe this answer much more).
'to assemble' becomes 'rally' (I've seen this in another clue).
'given' is a charade indicator (letters next to each other).
'o'+'rally'='ORALLY'
(Other definitions for orally that I've seen before include "How anyone would speak" , "How one speaks" , "By (word of) mouth" , "via the trap" , "as auditions are done" .)