Plagues have a way of stripping away what is superfluous, revealing the naked truth.
That might not be obvious from the text. On the surface, it seems like a clash between pharaoh and Moses, who has God on his side. The clue is in the plagues themselves. Bloody water, boils, hail, and locusts, among others, may seem like the perfect things to inflict as plagues. But biblical commentators point out that they have one other thing in common: many of them are used in depictions of the Egyptian gods.
For example, a frog was how Heket, the god of fertility, appeared in ancient Egyptian art. Frogs were viewed as sacred objects (see here and here). In making the frogs appear, God was demonstrating His superiority to this false God. The elimination of the plague of the frogs, God affirmed His supremacy: ultimately it was He who was the source of life, not the Egyptian fertility god.
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