Yeats opens "The Second Coming" with an image of a falcon escaping the falconer, swinging outward in a "widening gyre" -- a term Yeats coined to describe a circular path or pattern. As the falcon flies in great arcs away from the falconer, so the world spins out of control. The "gyre" was Yeats' symbol of a human epoch of 2,000 years. The poem frames a 2,000-year historical progression, with the birth of Christ marking the beginning and the war marking the end.
The remainder of the first stanza, after the "widening gyre," deals with symbols of destruction and death. "Things fall apart," says Yeats, and "Mere anarchy is loosed upon the world." He uses the symbol of a tide, "blood-dimmed," drowning innocence, that destroys hope and from which humanity needs salvation.
The Second Coming
Yeats introduces the symbol of the second coming in the second stanza, which is used as an answer to the first. The destruction of the first stanza must stand for something, and Yeats sees it as heralding a new epoch, or gyre. Yeats draws on the language of the Book of Revelation to conjure an image of Christ's return. He further included biblical symbolism when explaining that for 2,000 years (one gyre), the sleep of the Sphinx was "vexed to nightmare by a rocking cradle," presumably of the Christ-child.
As soon as Yeats introduces the idea of a Second Coming as salvation, he uses his most powerful symbol -- the Sphinx -- to offer his prediction of the future of the world and of humanity. As soon as he alludes to Christ, a "vast image" of a pagan religion appears to wander toward Bethlehem. The symbol here is of the end of a religion that, for Yeats, embodied hope and innocence. Its power is gone, and the hour of the "rough beast" -- the Sphinx, an allusion to pre-Christian religion -- has come around again.