God gave Moses a sign with his staff, which became a serpent and then returned to a staff. God also gave a sign with Moses’ hand becoming leprous and then being restored. A third sign was promised: water from the Nile would become blood on dry ground (Exodus 4:2-9).
In Exodus 4:1–7 Moses worries that the Israelites will dismiss his message and deny that Yahweh appeared to him. In response, Yahweh gives two concrete demonstrations: Moses’ staff becomes a snake and then returns to a staff, and Moses’ hand becomes diseased-looking and then returns to normal. This scene continues the back-and-forth at the burning bush, where Moses raises objections and Yahweh answers them with instructions and assurances. Immediately before this, Yahweh has told Moses what to say to Israel and how the leaders will respond.
Exodus 4:1–7 presents a credibility crisis and God’s response. Moses expects Israel to reject his message and deny that Yahweh appeared to him (explicit in verse 1).
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with Exodus 4:2-9, then read the surrounding section so the answer stays connected to the passage's flow.
2Yahweh said to him, "What is that in your hand?" He said, "A rod."
3He said, "Throw it on the ground." He threw it on the ground, and it became a snake; and Moses ran away from it.
4Yahweh said to Moses, "Put forth your hand, and take it by the tail." He put forth his hand, and laid hold of it, and it became a rod in his hand.
5"That they may believe that Yahweh, the God of their fathers, the God of Abraham, the God of Isaac, and the God of Jacob, has appeared to you."
6Yahweh said furthermore to him, "Now put your hand inside your cloak." He put his hand inside his cloak, and when he took it out, behold, his hand was leprous, as white as snow.
7He said, "Put your hand inside your cloak again." He put his hand inside his cloak again, and when he took it out of his cloak, behold, it had turned again as his other flesh.
8"It will happen, if they will neither believe you nor listen to the voice of the first sign, that they will believe the voice of the latter sign.
9It will happen, if they will not believe even these two signs, neither listen to your voice, that you shall take of the water of the river, and pour it on the dry land. The water which you take out of the river will become blood on the dry land."