Musar к Берешит 5:5

Regarding involuntary manslaughter, discussed in 21,13, the penalty of exile to a city of refuge parallels Adam's expulsion from Eden. Adam's sin had been due to the serpent's power to seduce. This had resulted in death being introduced in the universe (Genesis 2,17). When the Torah writes here מכה איש, when a man kills, it means Adam who was the first איש, individual, to cause death. Anyone who causes death is subject to "you are dust and to dust you shall return" (Genesis 3,19). The repetition of the expression מות תמות, in Genesis 2,17, is our clue to transmigration of souls, to the concept that several re-incarnations may be necessary for man to achieve his תכלית, his allotted task on earth. However, the principal meaning of the line was never that death would occur immediately after the sin had been committed. After all, Adam was 930 years old before he died (Genesis 5,5). His sin was comparable to an inadvertently committed act since it had been due to the outright seduction by the serpent. This is the reason a person guilty of involuntary manslaughter only has to be exiled to a city of refuge.