What's the theme of " Address to the Slaves of the United States of America" by Henry Highland Garnet?

In my opinion, the major theme of this speech is that
slaves need to rebel against the system of slavery.  Garnet did not necessarily mean
that slaves should actually rebel violently, but he did advocate that they should resist
their oppressors.

The point here is that Garnet is not
telling slaves to make the best of their situation.  He is also not telling them to wait
until someone else comes to rescue them from slavery.  In other words, he is not telling
them to hope for abolitionists to get them freed.  He is telling them to take it upon
themselves to gain their freedom.

So I think what is
distinctive about this speech, its main theme, is the idea that slaves themselves must
get up and do something to free themselves.

Here is a quote
to support this:

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Let your motto be resistance!
resistance! RESISTANCE! No oppressed people have ever secured their
liberty without resistance.