The Plague
The plague itself is thematic. Depending on the perspective of the reader, the plague of the novel could relate to the fascism and Nazism of World War II and the French Resistance, a more universal application to the plague of oppressive governments or an even more universal application of the oppression suffered by a minority for no apparent reason. It could also, of course, be the most concrete version of itself—a microbe, insidiously permeating every aspect of life and reminding people that they are subject to the forces of biology and nature just as much as they are subject to politics and economics.
The Absurd
The plague that strikes Oran is thematically rich in its exploration of the absurd. The location of Oran is utterly random yet the manner in which the plague plays out is utterly ruthless, almost as if it had been chosen by some greater power. This is the very essence of existential angst which the novel is dedicated to portraying. The plague does not care about politics, money, power, past sufferings, or morality; it simply is, and it is all-encompassing. People's wishes, dreams, fears, philosophies, and plans are all proven irrelevant. Dealing with the absurd is not something most people have experience with, and Camus chronicles the various ways they confront the absence of all reason.
Imagination vs. Abstraction
Imagination in the context of the Camus' plague means identifying with people, with giving into love and grief, with confronting the real. Abstraction is seen as deadening oneself to reality and mankind, sticking with statistics or philosophies or doctrines, focusing too much on rules or theories or putative panaceas. The characters in the plague span these binaries, demonstrating the multifarious responses to a trauma like the plague.
Religious Faith and Atheism
Rieux and Paneloux represent two poles of thought. As an atheist, Rieux finds it unfathomable that a God could allow the suffering seen in the plague and still be considered loving. He thinks it is a waste of effort trying to figure out why God would send the plague or what the sins were that necessitated the plague, and that the way one helps combat the plague is not by praying.
Paneloux initially sticks to standard Christian doctrine and sees the plague as God's censuring of human sin, but once he spends time on the ground among the ailing and the dying, he changes his understanding of his God. He does not renounce his faith but sees his choice as all or nothing, as the complete relinquishment of any claim to answers or comprehension and instead the resting in God's ultimate mysteriousness.
Camus presents both of these perspectives as valid, though his personal sympathy is with Rieux, and shows that every single person tries to come to terms with the plague whether it is through religion, philosophy, volunteering, suffering, or other methods and means.
Individuality
In the beginning, the townspeople of Oran are still caught up in their own lives—their loves, their pursuits of leisure, their past and future, their unshakeable sense of themselves as the center of the universe. However, as the plague takes over everything, they lose that sense of uniqueness and individuality. They are just like everyone else; they have no distinguishing characteristics. Their present is the same, their pasts all superfluous, their futures all suspended. Within this new collectivity there is some comfort, but there is also an acute loss of what makes being alive so wonderful.
Exile
One of the most terrifying, incomprehensible, and deadening aspects of the plague is exile—in all its capacities. People are exiled physically from their loved ones and trapped inside the walls of Oran. They are emotionally estranged by the inability of language to convey the reality of what they are experiencing. Those who fall ill or who have family members fall ill are isolated in camps and hospital wards, kept away from the healthy and deemed a threat. Many are exiled from God, no longer able to reconcile the suffering they experience and see with the promises of Christianity. They are exiled from the past and the future, stuck in an interminable future. There is only plague, and they are stuck in its void.
The Need to Bear Witness
At the end of the novel, Rieux identifies himself as the author of the chronicle and explains his conviction to bear witness to the plague. He needed to account for the ways life was disrupted, for the lives that were lost, for the quiet acts of heroism, for the endurance and the resilience and the charity and the overwhelming will to live. If no one documents, then no one remembers. Rieux isn't a perfect narrator, and as a doctor he knows he cannot save everyone, but he can make sure he contributes to the collective memory.
