What are some of the important themes in the Jourdon Anderson Letter?

I assume that you are talking about the letter that is in
the gmu.edu link below.  There are many important themes in this letter.  Some of them
include:

• The idea that some slaves, at least,
  were somewhat inclined to feel affection for their former masters.  Anderson tells his
  former master that he feels affection for him even though Col. Anderson was shooting at
  him when they were last together.  He feels this way even though he was enslaved for 32
  years.  This is very interesting because we often would not think of slaves having any
  affection for their masters.


• Lingering distrust that
  balances the affection.  Anderson's letter is full of ambivalence.  He expresses
  affection, but it is also very clear that he does not trust his former
  master.


• The prevalence of sexual violence towards slave
  women.  You can see this at the end of the letter where Anderson hopes for some
  reassurance that his daughters would not be treated like Matilda and Catherine
  (presumably older daughters) were.


• Pride.  Anderson is
  clearly a proud person.  He values the work that he did while enslaved.  He values
  himself and his dignity and that of his family members.  This pride endured through all
  those years of slavery.

In these ways, this
letter gives us a real window into the attitudes of former slaves soon after the end of
the Civil War.