The two tribes were privileged from among the non-Meccan...
The two tribes were privileged from among the non-Meccan Arab tribes by honor of their defense of the Holy Messenger and his message after the Hijrah. Had other tribes wanted to share with the two tribes this honor they could have acquired it; unfortunately they chose to oppose the Messenger instead of assisting him. Thus the continuity of the faith of Islam was connected to these three small groups.
The presence of the rest of the tribes and clans was dispensable and less than incidental ( 1 ) Al-Shareef Al-Radhi Mohammad Ibn Al-Hussein Nahjule- Balaghah collection of words of the Imam Ali Part 3 pp. 8-9. in relation to the faith of Islam in that period. For the presence of those clans and tribes had a negative effect and was fraught with dangers which threatened the life of the Messenger and his message.
ABU TALIB As we find these three small groups connected strongly with the message of Islam the history of this faith presents to us two men whose existence was indispensable and necessary during the period of Prophethood. One of these two men was Abu Talib uncle of the Messenger his guardian during the days of his childhood and his main defender after the commencement of his Prophethood.
The protection by this hero of his nephew and his defense against the threats of the Qureshites (the non-Hashimite Meccan clans) was a main factor in the continuity of life of the Messenger and his message. The Meccan clans were burning with hatred towards the Messenger and anxious to shed his blood. What prevented them from that was the presence of Abu Talib the chief of Mecca who led the Hashimites and made out of them and himself an unpeakable fortress around the Messenger.
The readers of the Islamic history know how the Qureshite clans delivered to Abu Talib an ultimatum to stop his nephew from defaming their fathers and belittling their gods and ridiculing their minds; otherwise they would confront him and Mohammad on a battlefield until one of the two parties perished. Abu Talib did not have any doubt that his acceptance of the Qureshite challenge meant his death and the annihilation of his clan; yet he did not pressure his nephew to stop his campaign.
He only informed him of the Qureshite ultimatum and then he told him kindly: "Save me and yourself my nephew and burden me not with what I cannot bear.".