Symbolism, Imagery, Allegory
Bunyan's text, written in 1678, is Franklin's favorite book. It's also a famous allegory about how Christians can make it through the hard parts of life in order to get to heaven. (If you'd like to learn more about it or how it works as an allegory, check out this cool lecture given by Ian Johnston.) It also acts as his benchmark for what a really good book is, a kind of ideal to which Franklin aspires. So, Pilgrim's Progress serves to tell us both what kind of reader Franklin is and what kind of writer he wishes to be.
As one of our beloved college professors taught us, we can also think of the Autobiography as a modified Pilgrim's Progress. Franklin has to pass through the Valley of Shadow (Boston), conquer Vanity Fair (his work on virtue), etc., to help establish a new Celestial City in Philadelphia. While Bunyan's Christian just wants to get to his Celestial City, which is really heaven, Franklin wants to help create his. This gets even more interesting when we think about how Franklin is a pious guy who believes in God, but doesn't really hang with organized religion. Perfecting Philadelphia – creating a militia, fire department, library, hospital, and university – is a way of creating a new kind of heavenly place, one where virtue is celebrated and many religions are practiced, and where the holiest thing you can do, perhaps, is read. (For more on Philadelphia, check out our section on "Setting.")