It was said in verse أَثُمَّ إِذَا مَا وَقَعَ آمَنتُم بِهِ ۚ آلْآنَ. It means: ` Would you believe when Divine punishment actually descends down upon you - whether at the time of death, or even before it? But, at that time, the response to your believing will be: آلْآنَ ('al'an: now?) meaning: Is it now that you have come to believe while the time of believing has already passed? This is similar to what the Pharaoh said while drowning: آمَنتُ أَنَّهُ لَا إِلَـٰهَ إِلَّا الَّذِي آمَنَتْ بِهِ بَنُو إِسْرَ‌ائِيلَ وَأَنَا مِنَ الْمُسْلِمِينَ ﴿90﴾ ("I believe that there is no god except the One in whom the Children of Isra'il believe - 10:90). In answer, it was said: آلْآنَ ('al'an: now?) and this believing by him was not accepted. In Hadith, the Holy Prophet ﷺ has said, ` Allah Ta` ala keeps accepting the repentance of His servant until he is seized by the agony of death.' It means that believing and repenting at the time of the agony of death is not credible in the sight of Allah. Similarly, in the mortal world, Taubah (repentance) could be accepted if done before the actual falling of the Divine punishment. Once the punishment strikes, Taubah is not accepted. The event related to the people of Sayyidna Yunus going to appear towards the end of the Surah in which their Taubah was accepted falls under this very rule. They had seen the punishment coming from a distance. Moved earnestly, weeping and wailing, they made their Taubah in all sincerity. Therefore, the punishment was withdrawn. Had it struck them, their Taubah would have remained unaccepted.