This surah is related to death of Hazrat kasim and Hazrat Abdullah who died at Mecca and infidels had joyfully expressed that the prophets were cut off and that with his death,he would be completly forgotten. They also alleged that the Prophet Muhammad (PBUH) had ccaused a cleavage among the Qureysh, and except for a negligeble few,all qureysh had ranged against him.
They also said that the new faith was inauspicious for the Prophet and it would not benifit him.Allah revealed this Surah to counteract their monostrous propaganda.