The conception of annihilation is a factor in human degradation, a cause of human debasement and lowliness, a source of human fear and abjection. It has been conducive to the dispersion and weakening of human thought whereas the realization of existence and continuity has upraised man to sublimity of ideals, established the foundations of human progress and stimulated the development of heavenly virtues; therefore it behoves man to abandon thoughts of non-existence and death which are absolutely imaginary and see himself ever living, everlasting in the divine purpose of his creation. He must turn away from ideas which degrade the human soul, so that day by day and hour by hour he may advance upward and higher to spiritual perception of the continuity of the human reality. If he dwells upon the thought of non-existence he will become utterly incompetent; with weakened will-power his ambition for progress will be lessened and the acquisition of human virtues will cease.

‘Abdu’l-Bahá, Bahá’í World Faith, p. 265-266

The spirit of man, however, can manifest itself in all forms at the same time. For example, we say that a material body is eithersquare or spherical, triangular or hexagonal. While it is triangular, it cannot be square; and while it is square, it is not triangular. Similarly, it cannot be spherical and hexagonal at the same time. These various forms or shapes cannot be manifest at the same instant in one material object. Therefore, the form of the physical body of man must be destroyed and abandoned before it can assume or take unto itself another. Mortality, therefore, means transference from one form to another -- that is, transference from the human kingdom to the kingdom of the mineral. When the physical man is dead, he will return to dust; and this transference is equivalent to nonexistence. But the human spirit in itself contains all these forms, shapes and figures. It is not possible to break or destroy one form so that it may transfer itself into another. As an evidence of this, at the present moment in the human spirit you have the shape of a square and the figure of a triangle. Simultaneously also you can conceive a hexagonal form. All these can be conceived at the same moment in the human spirit, and not one of them needs to be destroyed or broken in order that the spirit of man may be transferred to another. There is no annihilation, no destruction; therefore, the human spirit is immortal because it is not transferred from one body into another body.

‘Abdu’l-Bahá, The Promulgation of Universal Peace, p. 306