Homily:
literally, "sermon', but may include any serious talk, speech, or lecture involving moral and spiritual advice.

Example:
"He who is the religious advocate of marriage robs whole millions of its sacred influence, and leaves them to the ravages of wholesale pollution. The warm defender of the sacredness of the family relation is the same that scatters whole families... We have men sold to build churches, women sold to support gospel, and babes sold to purchase Bibles."
-Appendix, pg. 151, Narrative of the life of Frederick Douglass

Explanation:
This is an example of how Douglass created his autobiography, and especially the appendix, and homily. The purpose of this is to get his moral and spiritual beliefs across. These beliefs include the thought that slaveholders are hypocritical if they say they are Christians, and his main belief of the cruelty of slavery and how it should be abolished. These views are better seen, due to his use of homily. Another purpose of this is to get his thoughts across in a sophisticated and civil way, so more people would read and connect with it.