Pharaoh asked Moshe to pray to G-d to remove the frogs. Moshe Rabbeinu prayed and the frogs went away. The same thing happened with the plague of wild animals. Pharaoh suffered and begged Moshe and Aharon. They davened to Hashem and the wild animals left. Likewise, with the hail and the locust. Pharaoh begs Moshe to daven for him, Moshe davens, the hail stops, and the locust leave. Why was it necessary that every single time, Pharaoh would ask him to pray, Moshe would daven, and only then the plague would cease? The answer, says Rav Yerucham Levovitz zt”l (Mir Mashgiach) is that this narration teaches us something very fundamental about life: The way to obtain things in this world is to pray for them. This is the only way to achieve things in this world. Without prayer, not even Moshe could have prevailed.