وَأَنْ أَلْقِ عَصَاكَ
...
And throw your stick!
`the stick that is in your hand' -- as was stated in the Ayah,
وَمَا تِلْكَ بِيَمِينِكَ يمُوسَى
قَالَ هِىَ عَصَاىَ أَتَوَكَّوُا عَلَيْهَا وَأَهُشُّ بِهَا عَلَى غَنَمِى وَلِىَ فِيهَا مَأَرِبُ أُخْرَى
"And what is that in your right hand, O Musa!"
He said: "This is my stick, whereon I lean, and wherewith I beat down branches for my sheep, and wherein I find other uses." (20:17-18)
The meaning is: `this stick, which you know so well;'
قَالَ أَلْقِهَا يمُوسَى
فَأَلْقَـهَا فَإِذَا هِىَ حَيَّةٌ تَسْعَى
"Cast it down, O Musa!"
He cast it down, and behold! It was a snake, moving quickly. (20:19-20)
Musa knew that the One Who was speaking to him was the One Who merely says to a thing, "Be!" and it is, as we have already stated in (the explanation of) Surah Ta Ha.
And here Allah says:
...
فَلَمَّا رَاهَا تَهْتَزُّ كَأَنَّهَا جَانٌّ وَلَّى مُدْبِرًا
...
...
وَلَمْ يُعَقِّبْ يَا مُوسَى أَقْبِلْ وَلاَ تَخَفْ إِنَّكَ مِنَ الاْمِنِينَ
But when he saw it moving as if it were a snake, he turned in flight,
It moved so quickly, even though it was so big, and its mouth was so huge, with its jaws snapping. It swallowed every rock it passed, and every rock that fell into its mouth fell with a sound like a rock falling into a valley.
When he saw that:
...
وَلَّى مُدْبِرًا وَلَمْ يُعَقِّبْ
...
he turned in flight, and looked not back.
he did not turn around, because it is human nature to flee from such a thing. But when Allah said to him:
...
يَا مُوسَى أَقْبِلْ وَلاَا تَخَفْ إِنَّكَ مِنَ الاْامِنِينَ
O Musa! Draw near, and fear not. Verily, you are of those who are secure.
he came back to his original position.
Then Allah said: