The science of reincarnation establishes we are eternal spirit souls constantly traveling through different material bodies. Even in this life we are reincarnating from a child's body to a boy's body, then from a boy's body to a man's body. Similarly the time of death is simply a reincarnation into a different body. And next body is determined by our consciousness at the time of death. So it is very important to ensure our consciousness at the time of death is good. Otherwise our next reincarnation may be in an animal body.