Please give the explanation of the poem "The Second Coming" by William Butler Yeats.

The basic idea behind this poem is probably best summed up by the phrase "things fall apart."  The speaker in the poem seems to be worrying that the world is getting to be out of control -- the falcon is spiraling around, getting out of control of its owner, the center cannot hold, etc.

Furthermore, the speaker implies that there is nothing coming to save us.  The second coming, he says, surely must be coming.  But then he goes on to say that it is not.  Instead, some monster "slouches towards Bethlehem to be born."

So, what he seems to be saying is that the world is falling apart and there is nothing that is going to save us.