Although the souls of male and female are supposed to come into this world together, ever since the sin of the first man and woman this has not been so. They are divided when they emerge from above into this world. If the man does not have enough merit, he never finds his soulmate, and if he marries another his children are impure. Rabbi Elazar says that thousands of souls emerge simultaneously into the world, but they are not considered Nefashot until they settle in the body and receive their illumination from Malchut, this takes 33 days. He talks about the blood of purification and the blood of circumcision.