Introductory texts in literary anthologies and collections provide overviews and surveys of an author and his/her works, a literary era, literary style, and so on so forth. The explanatory footnotes enhance an understanding of the works in terms of contemporary culture and literary traditions in which the authors lived and wrote. Hence, the historical significance of the works.
These texts may be good readings to help you contextualize your writers/works and to prepare you for the scholarly articles in journals.