That you may warn a people whose forefathers were not warned, so (36:6)

Almuntakhab Fi Tafsir Alquran Alkarim

And you shall use it O Muhammad as the divine law expressing the will of Allah to warn a people whose fathers received no Messenger as a spectacle and a warning before; and they are oblivious of what they owe to Allah, to themselves and to the people at large

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(36:6) so that you may warn a people whose ancestors were not warned before wherefore they are heedless. *4

That you may warn a people whose forefathers were not warned, so meaning

*4) Another translation can be: "You should warn the people of the same of which their forefathers had been warned, because they live in heedlessness." if the first meaning, as given above in the text, is taken, the forefathers would imply the forefathers of the immediate past, for in the ancient time several Prophets had appeared in Arabia. And if the second meaning is adopted, it would imply this: Revive and refresh the message that had been conveyed to the forefathers of this nation y the Prophets in the past, for these people have forgotten it." Obviously, there s no contradiction between the two translations, and, as to meaning, each is correct in its own place!
A doubt may rise here: How could the forefathers of a nation to whom no warner had been sent at a particular time in the past, be held responsible for their deviation at that time? The nswer is: When Allah sends a Prophet in the world, the influence of his message and teaching spreads far and wide, and is handed down by one generation to the other. As long as this influence remains and there continue arising among the followers of the Prophet such people as keep his message of guidance fresh, the period pf time cannot be said to be without the guidance. And when the influence of the Prophet's teaching dies out, or the teaching is tampered with, the appointment of another Prophet becomes inevitable. Before the advent of the Holy Prophet the influence of the teachings of the Prophets Abraham, Ishmael, Shu'aib and Moses and Jesus (peace be upon all of them i could be seen everywhere in Arabia and from time to time there had been arising among the Arabs, or coming from outside, men, who revived their teachings. When the influence was about to die out, and the real teaching was also distorted, AIlah raised the Prophet Muhammad, and made such arrangements that his message can neither be wiped out nor tampered with. (For further explanation, see E N. 5 of Surah Saba above).
 

That you may warn a people whose forefathers were not warned, so meaning in Urdu

تاکہ تم خبردار کرو ایک ایسی قوم کو جس کے باپ دادا خبردار نہ کیے گئے تھے اور اس وجہ سے وہ غفلت میں پڑے ہوئے ہیں