That they may believe The sentence is imperfect, but the meaning is, This thou shalt do before them that they may believe. His hand was leprous as snow For whiteness. This signified, that Moses, by the power of God, should bring sore diseases upon Egypt, that at his prayer they should be removed. And that whereas the Israelites in Egypt were become leprous, polluted by sin, and almost consumed by oppression, by being taken into the bosom of Moses they should be cleansed and cured.
Related Commentaries of Exodus 4:5
Exodus 4:5-6
5 That they may believe that the LORD God of their fathers, the God of Abraham, the God of Isaac, and the God of Jacob, hath appeared unto thee.
6 And the LORD said furthermore unto him, Put now thine hand into thy bosom. And he put his hand into his bosom: and when he took it out, behold, his hand was leprous as snow.