Turning and turning in the widening gyre The falcon cannot hear the falconer; (lines 1-2)
The loss of social order has been a gradual process. It’s like when you wandered away from your mom in a crowded place as a small kid, and you thought you could still see her, but at a certain point you realized you were totally lost. The connection between the central authority of a society – be it the aristocracy or a republican government – has become weaker over the centuries. At a certain point, the link was lost completely, like a satellite spinning out of orbit.
The Second Coming! Hardly are those words out When a vast image out of Spiritus Mundi Troubles my sight (lines 11-13)
The Spiritus Mundi exists outside of space and time. It contains all the memories of the collective human past. The psychologist Carl Jung described a similar idea of the "collective unconscious," which may have been an inspiration to Yeats.
twenty centuries of stony sleep (line 19)
The speaker has a deep historical memory. He measures 2,000 years of history as merely one night of a baby’s sleep. Now that’s what we call "taking the long view" of things!