Exodus 4:7
And he said, Put thine hand into thy bosom again. And he put his hand into his bosom again; and plucked it out of his bosom, and, behold, it was turned again as his other flesh. And he said, Put thine hand into thy bosom again. And he put his hand into his bosom again; and plucked it out of his bosom, and, behold, it was turned again as his other flesh.
The sign belongs to the meeting near Horeb, the mountain of God, where Moses saw the burning bush, heard God call him by name, was told to remove his shoes because the ground was holy, heard God declare Himself the God of Abraham, Isaac, and Jacob, and hid his face from fear of looking upon God. The signs were given to Moses in Midian when he pleaded for a sign that the message given to him was from heaven. God gave this sign in answer to Moses' plea that Israel would not believe him nor listen to his voice but would say the Lord had not appeared to him.
The verse shows Moses' hand, made leprous as a sign, being restored when he put it into his bosom again, becoming again as his other flesh. The healing of the hand was given together with the rod becoming a serpent. The restoration assured Moses that the Israelites and Pharaoh would be convinced that one mightier than Egypt's king was manifest among them. The restoration assured Moses that God's power would be displayed through him, would make the Egyptians and Pharaoh fear, and would show that a greater power than Moses was at work.
By such signs and wonderful works God would cause Pharaoh and the Egyptians to fear so they would not dare harm Moses, and would convince the king and his people that one greater than Moses was manifesting power before them. The signs given to Moses serve as a precedent for asking God for a sign confirming a message from heaven.