Al-A'raaf 7:112

أَرْجِهْ

("Put him off"), means, "delay him (for a time)."

وَأَرْسِلْ فِى الْمَدَآئِنِ

("and send to the cities"), areas and provinces of your kingdom -- O Fir`awn,

حَـشِرِينَ

("to collect") to gather magicians from various lands. 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,

فَلَنَأْتِيَنَّكَ بِسِحْرٍ مِّثْلِهِ فَاجْعَلْ بَيْنَنَا وَبَيْنَكَ مَوْعِداً لاَّ نُخْلِفُهُ نَحْنُ وَلاَ أَنتَ مَكَاناً سُوًى

قَالَ مَوْعِدُكُمْ يَوْمُ الزِّينَةِ وَأَن يُحْشَرَ النَّاسُ ضُحًى - فَتَوَلَّى 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. Allah said,

Tafsir Ibn Kathir (abridged, English).