What does Frederick Douglass mean when he says "Bread of Knowledge"?

Douglass' use of the word "bread" suggests that knowledge
is as necessary to human life as is food.

Furthermore,
Douglass is clearly playing upon his readers' knowledge of the Bible. (His memoir was
intended as an argument against slavery.) In the Bible, references to bread in the New
Testament are numerous, and Jesus' body itself is equated with bread, among other
things.

The Lord's Prayer is Jesus' own words in which he
asks for "our daily bread"--the stuff of life here are again directly equated to our
spiritual well-being.

Therefore, bread, and by metaphor,
knowledge, take on a sacramental, holy quality for Douglass, and, he hopes, in the minds
of his readers.

Knowledge, for Douglass and his audience,
is not merely a matter of literacy, it is also about becoming fully human, and fully
capable of developing spiritually, morally and emotionally.