Then Moses answered and said, “But suppose they will not believe me or listen to my voice; suppose they say, ‘The LORD has not appeared to you.’ ”
So the LORD said to him, “What is that in your hand?”
He said, “A rod.”
And He said, “Cast it on the ground.” So he cast it on the ground, and it became a serpent; and Moses fled from it. Then the LORD said to Moses, “Reach out your hand and take it by the tail” (and he reached out his hand and caught it, and it became a rod in his hand), “that they may believe that the LORD God of their fathers, the God of Abraham, the God of Isaac, and the God of Jacob, has appeared to you.”
Furthermore the LORD said to him, “Now put your hand in your bosom.” And he put his hand in his bosom, and when he took it out, behold, his hand was leprous, like snow. And He said, “Put your hand in your bosom again.” So he put his hand in his bosom again, and drew it out of his bosom, and behold, it was restored like his other flesh. (Exodus 4:1-7)
Moses was applying for the job of “rescuer from slavery” for the people of Israel. Both the slave master, Pharaoh, and the enslaved people would be wanting references. Neither would have any particular reason for believing Moses when he showed up and said, “Let my people go.” The references God gave Moses to prove that he was a legitimate spokesperson for God were therefore what you might expect: miracles.
Moses responded as any human being might to the unexpected appearance of a snake: he ran away from it. After all, the most common human phobia is a fear of snakes. Moses could now turn his shepherd’s staff into a snake, or pick it up and turn it back again. Likewise, he could take his hand and make it diseased with one of the most feared diseases in the ancient world and then, just as easily, make the disease go away. Leprosy scared people because of the consequences of the disease: disfigurement, banishment from one’s family and community, and the loss of any way to make a living. God had given Moses power over what people feared most. God was reiterating for Moses that he had nothing to be afraid of at all.