The abject is outside the 'symbolic order,' and being forced to face it is an inherently traumatic experience. For example, when coming face to face with a corpse, a person would almost certainly be repulsed by it because they have been forced to face and object which has been cast out of the cultural world, having once been a subject. To confront a corpse that is recognised as a human (something that should be alive, but isnt) is to confront the reality that we are capable of existing in the same fate.
The abject/ abjection is our reaction to the threatened breakdown in meaning caused by the loss of distinction between the subject and object or by self and other.
Kristeva associates the abject with the eruption of The Real into our lives. She particularly associates this reponse with our rejection of death's materiality. Kristeva is careful to differentiate between the knowledge or the meaning of death, from the traumatic experience of acutally being confronted with the materiality that traumatically shows you your own death.
As Kristeva puts it, "The corpse, seen without God and outside of science, is the utmost of abjection. It is death infecting life. Abject."
The 'Abject,' for Kristeva is closely related to religion- the various means of purifying the abject , make up the history of religions.