Why is franklin’s “the way to wealth” often referred to as a “secular sermon”? a. it's meant to be read aloud to an audience. b. it presents a system of ethical behavior through proverbs. c. it motivates its audience through descriptions of the afterlife. d. it uses religious stories and imagery to communicate modern ideals.

I also think the correct answer is D. It uses religious stories and imagery to communicate modern ideals.
Secular means related to this world, something that doesn't have anything to do with religion or the Church. So I guess the final option best fits that description given that Franklin's speeches weren't intended to be religious, but rather didactic and teach people proper behavior. 

D. It uses religious stories and imagery to communicate modern ideas.