Allah tells us that He sent Musa, peace be upon him, and his brother Harun to Fir`awn and his chiefs with decisive evidence and definitive proof, but Fir`awn and his people were too arrogant to follow them and obey their commands because they were human beings, just as previous nations had denied the Message of the human Messengers. They were of a similar mentality, so Allah destroyed Fir`awn and his chiefs, drowning them all in one day. He revealed the Book to Musa, i.e., the Tawrah, in which were rulings, commands and prohibitions, after He had destroyed Fir`awn and the Egyptians and seized them with a punishment of the All-Mighty, All-Capable to carry out what He wills. After Allah revealed the Tawrah, Allah did not destroy any nation with an overwhelming calamity; instead, He commanded the believers to fight the disbelievers, as He says:

[وَلَقَدْ ءَاتَيْنَا مُوسَى الْكِتَـبَ مِن بَعْدِ مَآ أَهْلَكْنَا الْقُرُونَ الاٍّولَى بَصَآئِرَ لِلنَّاسِ وَهُدًى وَرَحْمَةً لَّعَلَّهُمْ يَتَذَكَّرُونَ ]

(And indeed We gave Musa -- after We had destroyed the generations of old -- the Scripture as an enlightenment for mankind, and a guidance and a mercy, that they might remember.) [28:43]

[وَجَعَلْنَا ابْنَ مَرْيَمَ وَأُمَّهُ ءَايَةً وَءَاوَيْنَـهُمَآ إِلَى رَبْوَةٍ ذَاتِ قَرَارٍ وَمَعِينٍ ]

(50. And We made the son of Maryam and his mother as a sign, and We gave them refuge on a Rabwah, Dhat Qarar, and Ma`in.)