Exodus 7:23

And Pharaoh turned and went into his house, neither did he set his heart to this also.

Exodus 7:23 belongs to the first plague, which struck the Nile because the Egyptians revered the river and its fish as objects of worship, treating the river as a god and crediting it with sustaining their lives and crops. Before the plague was brought, Moses and Aaron faithfully told Pharaoh its nature and effect, that he might have the privilege of saving himself from it by letting Israel go to sacrifice to God. Moses struck the water before Pharaoh, and it became putrid blood that continued for seven days, the fish died, and the people could not use the water.

The Egyptian magicians imitated the sign, so Pharaoh believed the miracles were done by magic and dismissed them. Pharaoh turned and went into his house, unmoved and without setting his heart to the plague even while it continued on the waters seven days; he refused to listen to Moses and Aaron and despised their words, hardened his heart and humbled not himself to heed God. He even continued his regular visits to the river to praise it and give thanks for its supposed power. Instead of repenting, his hard heart increased his hatred of the Israelites, and his refusal brought the judgment upon himself, though he had no power to harm Moses and Aaron.

The plague was directed against that reverence to show that the Egyptian idols could not protect them and that the Nile had no divine power to save its worshipers. In contrast to the imitated signs, the later removal of the frogs gave abundant proof the work was not magic but a judgment from the God of Heaven. God did not make the frogs vanish in a moment back to dust, lest the king and the Egyptians call it magic like the magicians' work, but let them die where they were and be gathered into heaps with their bodies lying in sight and corrupting the atmosphere. That evidence their vain philosophy could not explain away was given to the king and all Egypt.