Christadelphians hold a doctrine of conditional immortality: humans do not possess an immortal soul that survives death. At death, the person ceases to exist in any conscious form — body and 'soul' (understood as the breath of life, not a separate immaterial substance) return to the dust. The dead 'know nothing' (Ecclesiastes 9:5) and are in a state of complete unconsciousness — soul sleep — awaiting the resurrection.

Immortality, in Christadelphian teaching, is not inherent to human nature but is a gift conferred at the resurrection to those judged worthy. At Christ's return, the responsible dead (those who have been exposed to the gospel and accepted or rejected it) will be raised for judgment. The faithful will receive immortality and inherit the kingdom; the unfaithful will be destroyed (see hell entry). Those who died without ever hearing the gospel are not held responsible in this way.

This doctrine of soul sleep and conditional immortality distinguishes Christadelphians sharply from most Christian traditions, which hold to the natural immortality of the soul and conscious existence after death. Christadelphians regard the belief in an immortal soul as a pagan philosophical import — traceable to Plato — that corrupted Christian teaching. They see their position as a recovery of the Hebrew biblical understanding of the human person as a unified mortal being.