Shavua Tov. The Kuzari and the של״ה share the same idea but from a different perspective. Both point out that the reason the Torah only names one of the offspring of each generation, is because only one proved to be worthy and somewhat righteous. The של״ה explains this lack of righteousness as due to the pollution caused by the serpent. This connected these souls to the סטרא אחרא, or the side of evil, that caused them to gravitate towards evil. This was even true of Cain and Abel. Cain's soul was affected negatively by the serpent while Abel was not affected and was righteous. The של״ה adds that this explains the reason for Shatnez. The linen is connected to Cain and the evil that he possessed. And the wool is connected to Abel and his inherent goodness. Therefore, wool and linen must not be mixed in a garment worn by a Jew.