Whenever I think of powerful speeches and moving words, I always think of Dr. Martin Luther King Jr.'s "I Have a Dream" speech.
Here's the speech text: http://www.huffingtonpost.com/2011/01/17/i-have-a-dream-speech-text_n_809993.html
Here's a video of the speech: http://www.youtube.com/watch?v=B3P6N9g-dQg&feature=related
Why is it persuasive to me?
One of the main reasons I love this speech is the beautiful language that he uses. Even just reading the speech, it's poetic and abounding with figurative language. I especially think his use of parallel structure is powerful, for example, the "I have a dream" sequence. He paints images of places and people, and his syntax also works to strengthen his ethos. King wins me over with words.
The way he approaches his argument also appeals to me, and I think that he really considered the values of his audience. He clearly has patriotism and humanizes himself by talking about his own children. Whether people at this time would admit it or not, whether white or black, everyone shared some common values: love, family, kinship. King's speech is mostly based on rhetorical community, these shared core beliefs. There is a lot of very effective pathos. As well, I like that he alludes to the different parts of America, and our history- for example, his allusion to Abraham Lincoln.
His delivery of the speech is also powerful. The pauses he uses really let the words sink in, and his voice carries his emotions and asserts his beliefs. He intonates and emphasizes key points, and his tone has such a soul-rooted, hopeful strength.
For something to be persuasive to me, I have to find credibility in the speaker/writer, I have to value their argument, and I have to be emotionally moved on some level. Martin Luther King Jr.'s "I Have a Dream" speech accomplishes all of these things for me. It's a beautiful piece with a powerful and urgent message, calling Americans to action.