Exodus 4:20
And Moses took his wife and his sons, and set them upon an ass, and he returned to the land of Egypt: and Moses took the rod of God in his hand. And Moses took his wife and his sons, and set them upon an ass, and he returned to the land of Egypt: and Moses took the rod of God in his hand.
The time for Israel's deliverance had come, and Moses set out to deliver them, returning toward Egypt with his wife and his sons. He went forth as a humble shepherd with only a rod in his hand. On the way he consented to Zipporah's return to Midian so she would not have to witness the judgments that were to fall on Egypt, and she later rejoined him in the wilderness.
God's purpose was to pour contempt on human pride by working through lowly means. The rod was what God had given Moses for his work, and God would make it the symbol of His power. It was to become powerful in performing signs and wonders, delivering Israel from oppression and preserving the people when their enemies pursued them. It marked his authority as Israel's leader, a responsibility he could not lay aside until God released him.