From an organizational standpoint, the beauty of sermons is that each revolves around a specific theme. Accordingly, King could devote a single folder to each topic. He accumulated 166 folders, each with a title like “Loving your Enemies” (folder 1), “Why the Christian must Oppose Segregation” (folder 87), “Mental Slavery” (folder 113), and “The Misuse of Prayer” (folder 166). These folders contain King’s outlines; source material, like clippings from books; and drafts.
In addition to his card index, Martin Luther King, Jr. compiled a collection of 166 folders organized around various topics which he used to organize outlines, clippings, pages from books, and other source materials as well as drafts of sermons or speeches on those topics.
To some extent these folders are just larger format repositories mirroring the topical arrangements of his card index.