Douglass speaks about the ways in which slavery twists the ideas of what is decent and good. After his slave mistress, Mrs. Auld, teaches him the rudiments of reading, her husband, who has far more experience as a slave master than she does, roundly criticizes her. He says that reading will forever make a slave unfit for slavery.
Irony involves the use of something that is contrary to what one expects. Reading is a positive good, as is education, but in the slave-holding South, teaching someone to read becomes evil and even an offense, as it makes slaves begin to question their inhumane conditions and perhaps to want to escape. Douglass also uses the word "Christian" to show the irony of the twisted and inhumane way slaves are treated. A society in which teaching someone to read is an unjust society.