Then We sent Musa and his brother Harun, with Our Ayat and manifest authority, to Fir`awn and his chiefs, but they behaved insolently and they were people self-exalting (by disobeying their Lord). They said;
"Shall we believe in two men like ourselves, and their people are obedient to us with humility!"
So, they denied them both and became of those who were destroyed. And indeed We gave Musa the Scripture, that they may be guided.
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 مَأ أَهْلَكْنَا الْقُرُونَ الاٍّولَى بَصَأيِرَ 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