What does Allah Almighty mean by His saying: "{So We sent upon them the flood and the locusts and the lice and the frogs}"?

The noble verse that refers to the story of Moses (peace be upon him) with Pharaoh and his people is: "And they said, 'Whatever sign you bring us to bewitch us with, we will not believe you.' So We sent upon them the flood and locusts and lice and frogs and blood as distinct signs, but they were arrogant and were a criminal people." (Al-A'raf: 132-133)

Pharaoh's people said to Moses: We will not believe you, no matter what miracles you bring us. So Allah sent down punishments upon them: the flood (heavy rain and torrents), locusts (eating their crops), lice (fleas or weevils), frogs, and blood. These were clear signs of Allah's power and Moses' truthfulness, but they were arrogant and refused to believe, so Allah destroyed them. This is the recompense for the deniers and disbelievers.