In order to keep a true perspective as to where our success really comes from we need constant reminders. In this week's Parsha, the Torah tells us that for every thousand soldiers that went out to fight for the Jewish People, another thousand stayed in Eretz Yisrael and prayed for them. In other words, for each soldier at the front, there was another 'soldier' responsible to pray for his counterpart. You might that think that this was to give those at the front added protection. The real reason, however, was that those who were fighting shouldn't be under any illusion as to where their success was coming from.
Nothing lasts forever.
For this reason, the redemption from Egypt was not final, for it came 'at the hand of Moshe and Aaron' and for all their lofty spiritual height, they were no more than flesh and blood. However when Hashem redeems His people Himself, in His Glory and His Majesty, there will be no human imperfection in the redemption, and thus it will be complete and eternal. A staff is something inert, cut off from the tree from which it sprouted. It has ceased to have the power of furthering itself, of bringing forth new life. It will always remain what it is now.