The main idea in "The Second Coming" can seem elusive, especially because the poem ends with a complicated question that takes up the last five lines of the poem. However, an understanding of W. B. Yeats' concept of the "gyre" in line 1 can be helpful. Yeats believed history consisted of two-thousand-year cycles, and that at the end of the 20th century the current cycle would end and the next one would be ushered in. The current cycle in 1919 when the poem was written had begun with the birth of Jesus Christ. Yeats noted that he was living in a chaotic time--"things fall apart; the centre cannot hold." The world had just experienced the Great War, a wider spread and more deadly conflict than any that had previously occurred. Yeats, looking back on the current cycle, felt that it had regressed to the point where "the best lack all conviction, while the worst are full of passionate intensity." Thinking of the next 2000-year cycle, which he calls "the Second Coming," Yeats is filled with pessimism and dread. He imagines a "rough beast" rising from the sands in the desert and wonders what it is, but as seems clear from the description and the questions, he anticipates that nothing good can come in the next cycle. If the current cycle, as bad as it is, was kicked off by "a rocking cradle," a harmless if impotent event, then how much worse will be the next cycle, which is being heralded by this ominous beast? The main idea, then, seems to be pessimism about the current age and even more pessimism about the future.