This quote from "The Sieve and the Sand" section of the story is attributed to Thomas Dekker in the late 16th/early 17th century. Beatty is talking to Montag and knows that Montag is questioning their society and his role in it. Faber is also talking to Montag through the radio "seashell" in Montag's ear. The quote means that people value someone who has wealth and popularity, but is nothing more than a fool, more than they value a poor, honest, but good person. Or, flash wins out over substance. This is true of the society in which Montag and Beatty live. People don't care about substance or truth or other people even. They care about themselves and what they can have for themselves. Beatty is being ironic, but truthful here. He is, however, trying to manipulate Montag into thinking that Montag is wasting his time with trying to change society. Beatty means that no one will care that Montag is trying to do the good, honorable thing by bucking society; that people don't care about such things because there is nothing in it for them and that people would rather be entertained by flash than bothered by substance. Montag, with Faber's help, realizes that Beatty's words, while true, do not change the fact that Montag does not want their present society to continue.
This quote is spoken by Captain Beatty and is taken from an Elizabethan play called Old Fortunatus written by Thomas Dekker.
To put this quote into context, Beatty tells Montag that he had a dream about him. In this dream, Montag had read some books and was ready to "destroy authority." The two men then began exchanging famous literary quotes as each tried to justify his own position. This quote from Dekker is one of the quotes spoken by Montag in Beatty's dream.
Looking analytically at this quote, it states that society values a "gilded fool," a silly or uneducated person who is well-dressed, more than it values a "threadbare saint," a wise and good person who is not concerned with his appearance. In other words, society is more interested in and preoccupied with superficial matters than with deeper, more thought-provoking issues.
This quote aptly describes the world depicted in Fahrenheit 451. In this society, people are more interested in mindless forms of entertainment, like the parlor walls and driving fast, than learning, reading, and thinking.
For Montag, it is this attitude which provides the impetus for his rebellion and which drives his desire to destroy censorship and rebuild society.