Clearly, these are two drastically different articles. One is written by a man who is about to die for his crimes. Another is a legal document that provides a loophole to the fugitive slave law.
Yes, unfortunately, most legal documents are written in this obscure and difficult style--but why is that? Why is it so difficult to read them?
What strikes you about John Brown's speech? Would you have said anything different if you were in his shoes?