The Passing of Time
The Canticle For Leibowitz narrative occurs from the Cold War era through to 3756. Spanning nearly two millennia, the novel actively draws comparisons between future, past and present. Despite the passage of large amounts of time, several constants remain, including the legend of Leibowitz, the abbey in the desert, and the Catholic. Here Miller suggests that while time is a erosional force, it is possible for entities to live outside of a conceivable timespan. Furthermore, there is an element of repetitiveness to Miller's time scale. Nuclear warfare occurred in the 20th century, and again in the 37th century. This process has been referred to as "cyclical history." Therefore, will Miller suggests that certain entities evade time, it is also man's tendency to move towards destruction again and again.
Legacy
In an inadvertent way, A Canticle for Leibowitz is a powerful rumination on the nature of legacy. Miller establishes Leibowitz as the image of a productive lineage. His writings and thinking persists for centuries after his death and inspires continual evaluation. Leibowitz legacy resulted in the founding of the Albertian Order and eventually his own sainthood. In his lifetime, Leibowitz was not driven by lust for power or greed. He created his legacy through his passion for knowledge and his heroic fight against intellectual destruction. This is contrasted directly with the actions of state officials, who in their imperial and dominuative pursuits all but destroy the world twice over. Just like Leibowitz, Miller quietly suggests that the most influential legacies are not postured and contrived, but genuine and dedication action.
Humankind's Destructive Urge
Destruction is at the heart of A Canticle for Leibowitz. There is the destruction of cities, books, forms of knowledge, and whole societies. The entire novel is framed by the events of the Flame Deluge and the Simplification which all but erased the development of Earth. It takes a millennia and a considerable Dark Ages period for another form of normalcy to return, only for another nuclear showdown to occur. On a smaller scale, there is senseless violence like the murder of Brother Gerard. It is undeniable that Miller saw destruction, anger and competitiveness at the core of human nature.
Faith vs. Reason
A Canticle for Leibowitz presents an interesting view of religious life in that it is governed by intellectual sensibilities. During the Simplification when academics were slaughtered and whole libraries were burned, it was the Albertian Order of Leibowitz that sought to preserve all they possibly could. Contrary to the conception of faith as anti-intellectual, the Order worked rigorous academic study into the core of their operation. In this way, Miller suggests it is possible to be both objectively critical and spiritually faithful.
The Tenacity of Resurrection
Just as Miller writes of destructive and chaos, he is also deeply interested in the restorative, redemptive capabilities of humankind. Mirroring Christ's death on the cross, and resurrection three days later, Earth was slowly able to recover from the Flame Deluge. It is to be inferred that Leibowitz himself might be resurrected in the form of the Wandering Man in the desert. Furthermore, as the novel concludes and the world is heading again for nuclear fallout, the Order's spaceship leaves Earth, suggesting that life can begin again elsewhere. While humankind has a proclivity for chaos, A Canticle for Leibowitz suggests that resurrection is equally possible.
