Oh, Freedom is a post Civil War African American freedom song. I think it's an appropriate choice given the recent events in Arizona and the rhetoric of some politicians these days. I also think Baez's voice was made for this song.
One comment on the YouTube video pretty much sums it up.
katrinm61: "What a perfect voice and heart this woman has. For my youth, you spoke to me and kept me company on my journey with your songs. What a blessing to have lived in this time and hear such a marvelous voice and see a woman with such integrity as she grew up. Thank you for your music, your voice, your example."