Once again the dragon has failed to achieve his goal. He had thought to devour the child (Revelation 12:4) and so got expelled from heaven (Revelation 12:8–9). That expulsion already infuriated him greatly (Revelation 12:12). Now he is seeing even the earth (to which he had been thrown) also refusing to assist him but instead assist his enemy the woman. That frustration boiled over into a new level of fury.
17 Then the dragon became furious with the woman and went off to make war on the rest of her offspring, on those who keep the commandments of God and hold to the testimony of Jesus. And he stood on the sand of the sea.