What does Exodus 4:8 mean?
Moses knows that if he claims to be a messenger of God, others will doubt (Exodus 4:1). So, the Lord has established two miraculous signs. The first involves transforming Moses' staff into a snake (Exodus 4:2–5). The other instantly creates disease on Moses' hand, and just as immediately cures it (Exodus 4:6–7). The Mosaic law would later establish the need for two witnesses for important issues (Deuteronomy 19:15). That concept is foreshadowed in God providing more than one miracle for Moses to use.The purpose of the second sign is given here. The Lord notes that the second miracle "may" convince skeptics. Even when confronted with obvious divine power, some are inclined to skepticism. That's not always bad (1 John 4:1), but it can be a sign that they're opposed to truth, not seeking it (John 5:39–40). The Lord knows that some will dismiss the staff and serpent as a trick. Ignoring the afflicted and healed hand won't be so easy. But some may do so, anyway.
This also serves as a transition between the second and third signs (Exodus 4:9). This further proves Moses' mission and previews the first of the ten devastating plagues (Exodus 7:14–25). Pharaoh will be so hardened against God that only the most extreme suffering will cause him to submit (Exodus 12:29–32)—and only briefly (Exodus 14:8).