Moses and Aaron are tasked with trying to impress Pharaoh, but it seems that anything they do - staves to snakes, water to blood, a plague of frogs - Pharaoh's magicians can replicate. The lice is a different story: unable to conjure their own, the magicians proclaim it "the finger of god."
What's strange to me is that it's only when his own people are able to make a bad situation even worse that Pharaoh finds reassurance that Moses, Aaron, and the God of the Israelites are nothing to worry about. If it were me, I would find it reassuring if my crew could make things better.
The ability to destroy isn't a true demonstration of one's power; the ability to build is. Sometimes we are tempted to prove our prowess by bringing others down; a better way to prove one's worth is by raising everyone else up.