Pictures of the afterlife
For this set of imagery, the novel borrows from the Tibetan Book of the Dead which is a Buddhist scripture that details through allegory what the soul endures in the afterlife. This is the titular Bardo that Willie Lincoln finds himself having to pass through. The imagery suggests a universal problem, because all people die, and the question of how to get to the other side is described in imagery as Willie experiences the sublime domain of the Bardo.
Death and the supernatural
Needless to say the plot involves death and the afterlife, so there is also this well-developed imagery. For instance, much of the novel takes place in a cemetery because that is where the journey of the soul begins, basically. There are demonic tendrils that harrass the soul, making reincarnation less likely, and the spirits of the dead linger on the earth as ghosts, basically. The imagery is complete when Willie's dad, Abraham Lincoln, is assassinated and joins him in death.
Community and imagery
The imagery of community is explored through Willie's companionship with two dead men, Hans and Roger, and also through the mournful family he left behind. This imagery is also something that he wishes for some fulfillment in. He feels alone in death, and he is unprepared for the task of reincarnation. This makes him depend on the people around him, showing that the characters are a network.
Sickness and time
Time is depicted ironically when Willie gets a sickness that takes his life. The illness seemed all of a sudden, but afterward, the facts are concrete and irreversible, just like the passage of time itself. Time is offered (alongside illness and death) as an unavoidable part of life. The sickness that takes Willie's life is described as a cold that gets faster very quickly until he is unable to move, and then he dies. The description of death is a foreshadowing to Abraham's own death, the famous assassination by John Wilkes Booth.
