What point is Cervantes making when he lets Quixote have delusions of knighthood?

I think that Quixote was ahead of his time in articulating
the need for dreams in the individual subconsciousness.  Quixote is driven by the need
to be a knight.  It is a dream, a pursuit, embedded in his identity and allows Quixote
to appropriate the world in accordance to his own subjectivity.  This becomes part of
his character and when Cervantes creates it as such, the author is making a statement
that who we, as human beings are, is determined in large part by the dreams we pursue. 
Setting himself apart from previous authors on the world scene, Cervantes is suggesting
that our own visions and conceptions of self help to define our own reality, such as
Quixote.  This is also brought out in full force when the historical context of the
novel is revealed.  At a time when Spain's "Golden Age" was at its zenith, Cervantes
understood that while animated by individual dreams of conquest and glory, if one, like
Quixote, does not understand how external factors can impact individual subjectivity,
failure is almost assured.  Spain sought glory and conquest, akin to Quixote's pursuit
of the world of the knight.  Yet, the failure to understand the changing nature of the
world, such as the growth of industry, like Quixote's pursuit, ends up seeing a dream
become blighted.  The message is a complex one.  Dreams are a part of our identity, and
allow us to appropriate the world in accordance to our own subjectivity.  Yet, there are
limitations to this condition and failure to properly understand such limitations  can
result in personal destruction, seen in both Spain and Quixote.