Incendiary initiation ritual is a terrible ordeal for beginner (7,2,4)
I believe the answer is:
baptism of fire
'incendiary initiation' is the definition.
'baptism of fire' can be an answer for 'initiation' (I have seen 'Painful initiation ' mean 'baptism of fire' so perhaps 'initiation' could also mean 'baptism of fire'). I am not certain of the 'incendiary' bit.
'ritual is a terrible ordeal for beginner' is the wordplay.
I cannot quite see how this works, but
'is' is present in the answer.
'a' is within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for baptism of fire that I've seen before include "Difficult start" , "First experience of a difficult situation" , "Initiation ordeal" , "Initiating ordeal" , "First experience of a severe ordeal, especially a first taste of military combat" .)