/dɪsˈɔːdə(r)/: Absence of Functionality

"Men must not cut down trees. There is a God. (He noted such revelations on the backs of envelopes.) Change the world. No one kills from hatred.Make it known(he wrote it down). He waited. He listened. A sparrow perched on the railing opposite chirped Septimus, Septimus, four or five times over and went on, drawing its notes out, to sing freshly and piercingly in Greek words how there is no crime and, joined by another sparrow, they sang in voices prolonged and piercing in Greek words, from trees in the meadow of life  beyond a river where the dead walk, how there is no death." (24-25)

Septimus,a man hopelessly lost in a sea of PTSD, wastes away days of viewing horrific scenes around him. Since he is mentally scarred, he is using self-therapy to cure his illness. He writes short sentences. The simplicity of these sentences contrasts with the traumatic events that are acted out in his mind. The sentences start short but gradually crescendo into longer and more complex thoughts.This change represents how his mind functions. Although he visually sees casual live surrounding him, in his head it is examined as something connected to war or death, creating a more chaotic atmosphere in his thoughts.
There is also a religious connection in which he mentions "God...such revelations". Revelations, the last chapter in the bible, discusses death and the end of world with the coming of Jesus. So even when Septimus attempts to gather his attention to religion, death is continuously incorporated.
He contradicts himself with pure to dark diction. He references to the song of "sparrow" which is widely known to be of a sweet tune, but he uses "piercing(ly)" right afterwards. Empathizing the  contrast between he yearns for versus what his reality is.
PTSD, or Post Traumatic Stress Disorder, is a very serious and devastating illness that has unfortunately taken place in Septimus. Although he tries to cope with this disorder, it is hopeless because it has completely taken over the functionality of his brain.