Despite Nabi Musaa (alayhis salaam) having the powerful weapon of the Asaa (the Staff) which could instantaneously be transformed into a massive python which could devour Fir’oun and his armies, enabling Nabi Musaa (alayhis salaam) to either leave with Bani Israaeel without any hindrance or to capture the kingdom of Fir’oun and establish the Law of the Deen, this did not occur. On the contrary, the Mu’jizah of the Asaa was put to very limited use.
Primarily the purpose of the Staff was the protection of Nabi Musaa (alayhis salaam) and Nabi Haaroon (alayhis salaam) to enable them to continue with their Tableegh of the Deen which is the primary fundamental of Nubuwwat. The objective was not to kill Fir’oun and his people nor to impose Imaan on them by force. The objective was the propagation of the Deen and the willing acceptance of Imaan by the people. Allah Ta’ala says in the Qur’aan Majeed:
“If Allah willed, He would have gathered them all on the guidance (of Imaan).”
If it was Allah’s will that every person on earth be a Mu’min, like every Angel is a Mu’min, He had no need to despatch so many thousands of Ambiya and constrain them to undergo so much persecution and suffering in the execution of the mission of Nubuwwat. Allah Ta’ala had the power to create all people Believers. But His wisdom chose otherwise. He does not need the Serpent to ensure guidance for the people of Fir’oun. With His command the incorrigible kuffaar, namely, the Saahireen (Magicians) of Fir’oun accepted Islam and instantaneously became Auliya and Aarifeen. This was the effect of Allah’s Will and Power.
However, in terms of the Divine Plan, Imaan is not to be imposed on the people of the world by means of Mu’jizah. The Divine Plan ordains that people accept the Deen voluntarily, of their own free accord after seeing the Signs of Truth. Mu’jizah is a rare exception to bolster the Truth of the Nabi. Its purpose is not to force people to accept Imaan against their wishes.
Thus, Nabi Musaa (alayhis salaam) utilized the Mu’jizah of the Serpent only by the command of Allah Ta’ala to display a sign of his Truth, and for his protection against Fir’oun. As much as Fi’roun had attempted to apprehend and execute Nabi Musaa (alayhis salaam), he was unable to execute his plots since the Asaa was constantly guarding Nabi Musaa (alayhis salaam).
After the defeat of the magicians, when the Serpent directed its attention to Fir’oun and his followers, and pandemonium broke out, Allah Ta’ala commanded Nabi Musaa (alayhis salaam) to apprehend it and return it to its original form, the Staff. The time for Fir’oun’s punishment and destruction had not yet arrived. His fate was his doom in the Red Sea.