What is the relation or difference between a thesis and a theme?

In undergraduate study, a thesis is the defining idea of
an essay.  We usually think of it as the sentence that states the dominant idea of an
essay.  In an argument essay, for instance, the thesis directly states the argument the
writer makes.  It is up to the writer to support the thesis/argument with evidence,
etc. 

Theme, in contrast, is associated with fiction or
poetry rather than nonfiction.  Theme is the unifying subject or idea of a work.  It is
a subject or idea that is repeatedly revealed in a work, thereby unifying the work.  In
Shakespeare's Macbeth, for example, ambition serves as a theme, as
does the difference between appearance and reality.  These themes recur throughout the
play adding unity to the work.