Of what do they ask one another? (78:1) -Shakir
عَنِ النَّبَإِ الْعَظِيمِ
About the great event (78:2) -Shakir
الَّذِي هُمْ فِيهِ مُخْتَلِفُونَ
About which they differ? (78:3) -Shakir
Nay! they shall soon come to know (78:4). -Shakir
ثُمَّ كَلَّا سَيَعْلَمُونَ
Nay! Nay! they shall soon know (78:5). -Shakir
Excerpt from Tafseer of Agha Mahdi Pooya1:
Naba-il azim (the great news) here and in verse 67 of Surah Sad (38:67), refers to the vicegerency of man to represent Allah on the earth in order to exercise authority on His behalf, i.e. imamah or wilayah.
Hafiz Abu Nu’aym in Hilyatul Awliya says that the Holy Prophet told his companions: "Naba-il-azim (the great news) refers to the wilayah of Ali ibn abi Talib."
Refer to the commentary of Ma’idah, 5:67 for the wilayah of Ali ibn abi Talib. Therefore wilayah of Imam Ali is the decisive test of man's submission to Allah's authority. Man shall not be able to avoid or escape from acceptance of Ali's wilayah as verses 4 and 5 assert.
Imam Muhammad bin Ali al Baqir said: "Naba-il azim refers to Ali ibn abi Talib".
Alqama says that in the battle of Siffin a soldier came out from the army of Mu-awiyah and recited Ya Sin in front of Imam Ali. He asked him: "Do you know what is naba-il-azim?" He did not know. Ali said: "I am the naba-il azim." A similar event also took place in the battle of Jamal. Amr ibn As, an avowed enemy of Ali, once said:
"Ali is the naba-il azim. He is the babullah (the door through which one enters into the realm of the realisation of Allah)."