How does the traditional idea of the Second Coming differ from what the speaker is envisioning?

The fundamental difference in William Butler Yeats’s poem can be found in the penultimate line, where he queries the future birth of the “rough beast.” Through the first half, the speaker puts forward an apparently apocalyptic vision, with “anarchy,” “the blood-dimmed tide,” and “innocence . . . drowned.” Civilization is endangered, they indicate, as “the worst” people are the ones “full of passionate intensity.”
In the second stanza, the speaker seems to be hopeful of a radical change: “Surely the Second Coming is at hand.” This indicates that the speaker is looking for the return of Jesus Christ to solve the world’s problems. As they continue speaking, however, the vision seems no more encouraging than the problem just presented. The imagined being “troubles my sight.” Rather than any resemblance to Christ, the envisioned figure has a lion’s body and a “pitiless,” “blank” stare. As it moves among “indignant” birds, it calls to mind the “darkness” that has surrounded the world, in which “stony sleep” has brought a “nightmare.” This image leads to the question about the “rough beast”—by no means an advent of salvation.