This is the meaning of the verse, "It is your sins that separate you from your G‑d" (Isaiah 59:2); Kelipa which results from sin clothes the soul and stands between it and G‑d, preventing the flow of light. This idea is hinted at in the Talmud: "We learn that the snake came upon Eve and imparted zuhama [spiritual dirt] to her."1 (Avoda Zara 22b )

...the snake came upon Eve and imparted zuhama [spiritual dirt] to her.

This was the case for Adam as well, and all his descendants after him until the days of Moshiach, since they [their souls] were included in Adam at the time of the sin. Thus all people die "because of the bite of the snake," since all were affected by the zuhama. Nevertheless, not all souls are equal, because every soul was blemished according to its proximity to the sin.

Some limbs were more directly involved in the sin than others, and so were damaged more. E.g., the hands actually took the fruit, the mouth ate it, whereas the chest only derived nourishment.

However, all sins that people perform on their own, that is, other than the one that Adam committed, draws kelipa to them, depending upon the severity of the sin committed. However, a person’s teshuvah can push away the zuhama that came to him because of his sin, even in the case of very serious sins.

The dirt and the kelipot that bond with all souls as a result of the sin of Adam are not affected by teshuvah, necessitating death to rectify the defect. For even though G‑d accepted Adam’s teshuvah and granted him atonement, nevertheless the zuhama and kelipa remained with him as when he sinned. It only separates from us at death, since he committed a very serious crime, for many reasons that we will not explain here.

This is the secret of those who died [only] from the bite of the snake: Benjamin, Yishai, Kilav [one of David's sons – Ed.], Levi, and Joshua bin Nun who did not participate in the sin of the calf, as the Zohar says (Zohar I 53a, Shabbat 55b). In other words, even though they did not commit any sins, they still had to die, since the kelipa and zuhama adhered to them as a result of Adam’s sin and only leaves at death. This is also the secret of what the Sages mean when they refer to the zuhama of the snake that was imparted to Adam and Eve.

We need to explain why death causes a separation of the kelipot from man. First of all, kedushah [holiness] is called life. As it says, "See! I place before you life and good" (Deut. 30:15), and, "Those who adhere to G‑d your L-rd - all of you are alive today" (Deut. 4:4). This is because it is G‑d who gives sustenance and food to all of his creations.

...the kelipa cannot leave him until he dies...

However, the sitra achra, which removes [flow] from creations, is called death, as it says [in the former verse], "and death and evil". Thus when a person sins, he draws the sitra achra, called death, towards him. Therefore the kelipa cannot leave him until he dies, when the flesh rots in the soil. Then the kelipa that was tied to him leaves along with the kelipa from the zuhama that was imparted to Adam and Eve.

[Translation and commentary by Perets Auerbach.]