"That they bring to you all well-versed sorcerers."At this time, magic was the trade of the day and it was widespread and popular. They had the idea that what Musa brought was a type of magic similar to the magic that the sorcerers of their time practiced. Because of this incorrect assumption, they brought all the magicians in order to defeat the miracles that he showed them.Allah said about Fir`awn,لَنَأْتِيَنَّكَ بِسِحْرٍ مِّثْلِهِ فَاجْعَلْ بَيْنَنَا وَبَيْنَكَ مَوْعِداً لاَّ نُخْلِفُهُ نَحْنُ وَلَا أَنتَ مَكَاناً سُوًىقَالَ مَوْعِدُكُمْ يَوْمُ الزِّينَةِ وَأَن يُحْشَرَ النَّاسُ ضُحًىفَتَوَلَّى فِرْعَوْنُ فَجَمَعَ كَيْدَهُ ثُمَّ أَتَى Then verily, we can produce magic the like thereof; so appoint a meeting between us and you, which neither we nor you shall fail to keep, in an open place where both shall have a just and equal chance."(Musa) said:"Your appointed meeting is the day of the festival, and let the people assemble when the sun has risen (forenoon)."So Fir`awn withdrew, devised his plot and then came back. (20:58-60