The Story of the People of Nuh and the Lesson from it
Allah the Exalted said,
كَذَّبَتْ
(denied) `before your people, O Muhammad,'
قَوْمُ نُوحٍ فَكَذَّبُواْ عَبْدَنَا
(the people of Nuh. They rejected Our servant) means, they denied him categorically and accused him of madness,
وَقَالُواْ مَجْنُونٌ وَازْدُجِرَ
(and said: "A madman!" Wazdujir.) Mujahid said about Wazdujir: "He was driven out accused on account of madness." It was also said that Wazdujir means, he was rebuked, deterred, threatened and warned by his people saying:
فالْتَقَى الْمَاءُ عَلَىٰ أَمْرٍ قَدْ قُدِرَ (so the water [ of both kinds ] met together for a destined event....54:12). In other words, the rain water pouring down from the skies in torrents and also bubbling water gushing forth from under the ground, caused the Deluge [ a huge flood ] which engulfed the entire land, and thus the Divine decree was fulfilled, destroying the people of Nuh (علیہ السلام) to the last man, and even the peaks of the mountains could not give them any shelter.
Tazkirul Quran
Maulana Wahiduddin KhanOn ayahs 8–16
God causes such events to take place in the present world as make the occurrence of Doomsday understandable in advance. An event of this type occurred in the days of the Prophet Muhammad a few years before the Hijrah, when people saw that the moon was ‘cleft in two.’ At that time, the Prophet told the people that just as the moon had broken into pieces, the world would also break into pieces and then a new world would be built. Undoubtedly, there is a lesson to be learned from such events. But this is possible only when a man applies his mind to it. Those who are slaves to their own desires, will look at such events and simply say, ‘This is magic’. They will interpret such events as they please and treat them as inapplicable to themselves. For such people even the most cogent reasoning is meaningless. They will come to their senses only when the blast of Doomsday bursts on them and deprives them of the opportunity to reform.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.