3888. These two kingdoms are presented to view in man by means of the two kingdoms that are in him, namely, the kingdom of the will, and the kingdom of the understanding, which two kingdoms constitute the mind of man, nay, the man himself. The will is that to which corresponds the pulsation of the heart; and the understanding is that to which corresponds the respiration of the lungs. For this reason there are likewise in the body of man two kingdoms, namely, those of the heart and the lungs. He who knows this mystery may also know how the case is with the influx of the will into the understanding, and of the understanding into the will; consequently with the influx of the good of love into the truth of faith, and vice versa; thus how the case is with the regeneration of man. But they who are only in corporeal ideas, that is, who are in the will of what is evil and the understanding of what is false, cannot apprehend these things; for they cannot think of spiritual and celestial things otherwise than sensuously and corporeally, consequently not otherwise than from darkness of the things of heavenly light (or of the truth of faith), and from cold of the things of heavenly flame (or of the good of love). This darkness and cold so extinguish celestial and spiritual things that these appear to such persons to have no existence.