The knowledge of how to conceive a child is vital to bring forth good souls on earth for building a better world. Yogananda, the world-famous author of Autobiography of a Yogi, said: “At the time of physical conception, there is a flash of light in the ether. Souls in the other world that await physical rebirth, when the vibrations of that light are compatible to their own, rush towards it. Sometimes more than one soul enters a womb at the same time. Thus, twins are born.”  “For couples desiring spiritual children,” Yogananda continued, “it is important that they keep their consciousness uplifted when coming together in physical union. For their vibrations at that moment will determine the quality of the flash of light in the astral world.” (The Essence of Self-Realization: The Wisdom of Paramhansa Yogananda, p. 76)

To understand rebirth, one needs to accept the fundamental concept of consciousness or life as energy. We know that an individual’s physical body grows from infancy to youth, to middle age, and then to old age, yet the soul within the physical body, the "I" Consciousness, always remains unchanged. The fact that the physical body changes as time goes by, clearly shows that it is energy that causes the aging process. According to modern science, energy is indestructible. The Law of Conservation of Energy specifically states that energy can neither be created nor destroyed. Satyananda (1923–2002), one of the greatest spiritual masters of India, scientifically observed: “In recent research on dying, the experiences of those who have been revived after death have been recorded. It was found that they first entered into darkness and then felt agony and pain. They heard peculiar cries and screaming. After some time they found the darkness was diminishing and the light was growing little by little, just like a dawn of a new day…Then they returned again through the same darkness. Now, it is not the experience that is important here, but who experienced it. If a man was dead and nothing survived, how could he have this experience? This proves that the soul survives death.” (Building a Noble World, p. 12)

Just as 500 years ago, at the time of Columbus (1451-1506), not many people recognized the fact that the earth is round, so also many people today do not accept the fact that soul survives after death.  Describing the mystery of death, life after death, and reincarnation, Sivananda wrote: “This subtle body comes out with all its impressions and tendencies at the time of death of the gross physical body. It is like vapor. It cannot be seen by the physical eye. It is the subtle body that goes to heaven. It manifests again in a gross form. This re-manifestation of the subtle form into the gross physical form is called reincarnation. You may deny this law, but it exists. It is inexorable and unrelenting.” (Building a Noble World, p. 11-12)