لِتُنذِرَ‌ قَوْمًا مَّا أَتَاهُم مِّن نَّذِيرٍ‌ ( so that you warn a people to whom no warner has come before - 28:46). The expression ` a people' is purported here for the Arabs, who are the progeny of Sayyidna Ismail (علیہ السلام) . No prophet was sent to this ` people' after Sayyidna Ismail علیہ السلام until the Holy Prophet ﷺ was sent. The same subject will follow in Surah Yasin. But this verse is not in conflict with the other verse إِن مِّنْ أُمَّةٍ إِلَّا خَلَا فِيهَا نَذِيرٌ‌ (There is no community, but there has come a warner among them - 35:24). What the present verse means here is that there was no prophet in ` this people' for a long time after Ismail . But after the arrival of the Holy Prophet ﷺ this void was filled up.