To Bakhtin, the novel stands apart from earlier forms such as the epic or lyric poem because it includes a multiplicity of voices. It is polyphonic, or made up of a blend of voices and dialects. It functions by including a number of different perspectives and clashing points of view. Therefore, Bakhtin characterized the novel as dialogic. In contrast, an epic like Homer's Iliad has a unifying worldview.
Bakhtin's theory of the novel came to the forefront in the late 1970s, when many groups such as women, blacks, formerly colonized peoples, and other minorities were fighting to articulate their views on literature and through literature. The idea that the novel was not a unified whole but actually derived its form and power by including conflicting, often subaltern (oppressed) viewpoints appealed very much to sensibilities of the time period—and it still does.
Bakhtin makes the important point in "Discourse in the Novel" that novels have to be approached as wholes. To slice and dice and take one character's perspective—even if that "character" is the narrator—as representative of a novel's worldview is to do violence to the genre.