What are the main points in Raymond Williams' "Dominant, Residual, And Emergent"?

It's a bit ironic to ask the main points of "Dominant,
Residual, And Emergent" in Marxism in Literature, since the title of the selection
speaks so much for itself!  However, ... I would say (in expansion) that the main points
are explaining dominant ideology, residual ideology, and emergent
ideology.

The book itself has much more than this one
selection, including lots of contributors to Marxist theory (in addition to Marx) such
as Lukacs, Althusser, and Goldmann.  Further, Williams adds his own name to the list by
adding a new theory:  "cultural materialism" which adds Marxist theory to literature.  
Before he gets to the ideologies you ask about, he discusses things like determinism and
hegemony in literature at length.

But to get to the meat of
your question, these three ideologies you mention must be defined.  First, a dominant
ideology has to be espoused by most of society.  That is why it's dominant.  Even within
a dominant ideology, though, residual ideologies usually exist.  A residual ideology is
one that WAS dominant in a previous time period.  (Residual ideologies, then, are often
the current dominant ones that have been adapted to suit the current culture.)  Finally,
there are emergent ideologies which are completely new and in direct opposition with the
dominant ideology.  It is this "fight" between the dominant and the emerging ideologies
that makes change happen.

Thus, put into the context of
Marxism in Literature the selection entitled "Dominant, Residual,
And Emergent" is most instructive in understanding ideology.