What is the explanation of soul reincarnation in Upanishads?

Upanishads point out that after the death of the body, the soul will be reincarnated in the womb of another mother. The reincarnation of the soul goes through five stages: entering the moon and becoming rain; Rain falls on the earth and becomes food, and food becomes sperm after being eaten; Sperm enters the mother and fetus to form new life. This idea of "causal reincarnation" not only affects Asia, but also affects almost the whole world.