This was a proof from Allah for Musa and a great miracle. This was something that broke through the boundaries of what is considered normal, thus, it was a brilliant evidence that none but Allah could do. It was also a proof that no one could come with the likes of this (from mankind) except a Prophet who was sent (by Allah). Concerning Allah's statement,

وَمَا تِلْكَ بِيَمِينِكَ يمُوسَى

(And what is that in your right hand, O Musa) Some of the scholars of Tafsir have said, "He (Allah) only said this to him in order to draw his attention to it." It has also been said, "He only said this to him in order to affirm for him what was in his hand. In other words, that which is in your right hand is a stick that you are familiar with. You will see what We are about to do to it now."

وَمَا تِلْكَ بِيَمِينِكَ يمُوسَى

(And what is that in your right hand, O Musa) This is an interrogative phrase for the purpose of affirmation.

قَالَ هِىَ عَصَاىَ أَتَوَكَّؤُا عَلَيْهَا

(He said: "This is my stick, whereon I lean...") I lean on it while I am walking.

وَأَهُشُّ بِهَا عَلَى غَنَمِى

(and wherewith I beat down branches for my sheep,) This means, `I use it to shake the branches of trees so that the leaves will fall for my sheep to eat them. ' `Abdur-Rahman bin Al-Qasim reported from Imam Malik that he said, "It is when a man places his staff into a branch and shakes it so that its leaves and fruit will fall without breaking the stick. It is not the same as striking or beating." Maymun bin Mahran also said the same. Concerning his statement,

وَلِىَ فِيهَا مَأَرِبُ أُخْرَى

(and wherein I find other uses.) This means other benefits, services and needs besides this. Some of the scholars took upon themselves the burden of mentioning many of these obscure uses. Concerning Allah's statement,

قَالَ أَلْقِهَا يمُوسَى

((Allah) said: "Cast it down, O Musa!") "Throw down this stick that is in your right hand, O Musa."

فَأَلْقَـهَا فَإِذَا هِىَ حَيَّةٌ تَسْعَى

(He cast it down, and behold! It was a snake, moving quickly.) This means that the stick changed into a huge snake, like a long python, and it moved with rapid movements. It moved as if it were the fastest type of small snake. Yet, it was in the form of the largest snake, while still having the fastest of movements.

تَسْعَى

(moving quickly.) moving restlessly. Concerning Allah's statement,

سَنُعِيدُهَا سِيَرتَهَا الاٍّولَى

(We shall return it to its former state. ) the form that it was in, as you recognized it before.