Like many of the novels which speak to the "human condition" and living life, the themes illuminated in Octavia Butler's novel Kindred are slavery, choices and consequences, appearance and reality, and the idea of differences.
Each of these themes are important when dealing, or examining, the issues related to slavery. The themes are highlighted through Butler's examination of Dana's perspective and understanding regarding the harshness and realities associated with slavery.
For Dana, her experiences with slavery come to be horrifying for her. The fact that slavery is much more oppressive and devastating than she realized speaks to the theme of the human condition.
As for any person, the choices they make in life have consequences. Therefore, the novel's highlighting of how choices and consequences affect both the characters involved and the reader alike is important to this theme.
As with any novel which examines how one perceives the world around them, the theme of reality and how things appear is important as well. This theme allows, again, both characters and readers to understand that not everyone sees the world around them in the same way.
The last theme, the theme of differences, is important based upon the fact that slavery is based solely upon differences. Slavery came about because of the perception that one race was stronger than the other and, based upon that, the "weaker" race could more easily be oppressed. The theme is illuminated through Dana's understanding and feelings of alienation based upon her differences.