Images of light and fire appear all over the novel, and they often go together. Makes sense, right? Strike a match, and, look at that—you get both fire and light.
The result is a symbol with a dual nature. The light aspect of the symbol represents knowledge, a very literal take on the concept of enlightening. The fire part of the symbol represents the destructive capability of that knowledge, in the same way that an uncontrolled fire can seriously wreck your day. Not to mention your house.
But we also need to consider the history of these symbols in other stories. A Canticle is not the first story to use light and fire in this way. It actually draws its inspiration from two famous mythological figures. Because, hey, if it's good enough for Shakespeare, it's good enough for A Canticle.
The first mythic figure is Prometheus. We won't go into all the details here—mostly because we went into them here. What's important to remember about Prometheus when reading A Canticle is the way fire represents knowledge, specifically forbidden knowledge—a.k.a. the awesomest of all knowledge.
Dom Paulo forges this link between fire and knowledge when he notes:
Now a Dark Age seemed to be passing. For twelve centuries, a small flame of knowledge had been kept smoldering in the monasteries; only now were their minds ready to be kindled. (14.2)
In this way, the symbol of fire in Prometheus is very similar to the Tree of Knowledge of Good and Evil from the Genesis story of Adam and Eve. That is, a god doesn't want humanity to grasp some forbidden knowledge, but humanity does just that through the help of another supernatural force.
Star Light, Star Bright
And speaking of that other supernatural force, let's discuss Lucifer, the second mythic figure. Lucifer's name is linked to light and fire two times in the novel. The first happens when the monk working the dynamo yells "'Lucifer!'" as he sparks the arc lamp (18.36).
At the same time, a library clerk mistakes the arc lamp for a fire (18.39). So the scene is a twofer, connecting the name with both light and fire simultaneously.
In Fiat Voluntas Tua, the Church's code word for nuclear weapons is "LUCIFER" (24.25). As you can probably guess, the boom of nuclear fission contains a whole bunch of light. And even more fire. Not to mention radiation and one crazy shockwave. Dude.
Of course, the word Lucifer is meant to suggest Satan, Abbadon, the Devil, the Beast, the Opposer, the Antichrist, and He-Who-Must-Not-Be-Named. Wait, the last one's Voldemort. Sorry, we get them confused sometimes. Point is, the dude's got a lot of names.
But A Canticle is diving deeper into the Lucifer myth than simply associating the word with the devil. The origin of Lucifer comes from the Latin meaning "morning star" or "light-bringer."
It's the Latinate name for Venus, because the planet appears in the east in the early morning before the sun rises. So it seems to bring forth the light of day (source). Let there be light.
Lucifer didn't become associated with the devil until later Biblical translations. When early translators needed a word for the Greek Phosphoros, they used Lucifer. As a result, Isaiah 14:12 reads:
How art thou fallen from heaven, O Lucifer, son of the morning! How art thou cut down to the ground, which didst weaken the nations!
Some Bible readers associated the passage with the fall of Satan from heaven and assumed Lucifer to be Satan's proper name. This is why we associate the two together today.
In actuality, the passage is about a Babylonian king, and Lucifer/Venus is being used as a metaphor for the heavenly heights he'll never reach as an earthly king—not as a proper name. Similarly, Bible readers would come to associate Satan with the trickster Serpent from the Garden of Eden.
These associations link the word Lucifer with all of the important aspects of light and fire in A Canticle. The word origin for Lucifer links it to light, the Serpent association with forbidden knowledge, and its connection to the figure of the devil with the idea of sin.
Whew. That was a lot. We know.
Here Comes the Boom
Let's get back to the symbol in the novel itself, and how light and fire represent knowledge in its dual capacity: the ability to enlighten, but also to destroy.
We see the ability to enlighten many times in the novel. When Francis creates his illuminated copy of the Leibowitz blueprint, he's literally illuminating a piece of knowledge that will enlighten later generations.
Brother Kornhoer's knowledge re-invents the arc lamp, and later illuminates the library for Thon Taddeo. This allows him to read the information stored in the Memorabilia.
And finally, building a spaceship, the Quo peregrinatur, allows the "small flame of knowledge" to be kept "smoldering" rather than be blown out by nuclear fallout. Get it—blown out by nuclear fallout? Okay, fine, it's not funny.
But the same knowledge that creates fire for light also creates the fire that burns. Thon Taddeo believes re-introducing scientific knowledge into the world will result in positive change, but that that change must first "'come to pass by violence and upheaval, by flame and by fury" (20.127, emphasis ours).
And then there's the big daddy of knowledge as fire: the nuclear bomb. When Zerchi describes the nuclear bomb that destroys the abbey, he focuses on the light and how it "[grows] bright and brighter until the booth was full of bright noon" (29.31).
The light itself takes on the attributes of fire, and even burns the confessional booth's curtain. In the end, the return of this type of scientific knowledge to the world ultimately destroys it. Boom. (Yeah, we said it.)