You should know that all the souls mentioned, like that of Rabbi Akiva and others like him, are from the root of Cain, which is from gevurot of hod of daat - the fifth gevura. Also, all the souls from gevurot of hod in the daat of Leah are related to the root of Rabbi Akiva - they are considered one root. You can draw a parallel from this to the root of Abel, which is from the chasadim of daat.

[This is] the issue of the Cain-root, and from it you can extrapolate and apply to the Abel-root.

The choicest special ones fell further down than all of the rest.

All the sparks of souls from the Cain-root were dependent upon Cain. When he sinned, all of them became mixed in the kelipot. The choicest special ones fell further down than all of the rest. Because the sin of Cain blemished the [level of] machshava elyona [i.e. supernal thought], as mentioned in Sefer HaTikunim, Tikun 69. The place of the soul-root Rabbi Akiva ben Yosef was the hands. In the secret of, "And his hand was holding the heel of Esau." (Gen. 25:26)

This verse is said about Jacob. Akiva shares the same letters of Jacob, for he came from him. Therefore was he so outstanding in Torah - the quality of Jacob.

The hands have the ability to go down as far as the heel or as high up as the head, unlike the rest of the limbs. Therefore, these limbs fell to the depths of the kelipot, until the heel. When Rabbi Akiva was killed, he ascended to the machshava helyona.

"The bigger they are - the harder they fall."

This is the secret of what G‑d told Moses [when Moses saw a vision of] the death of Rabbi Akiva, "Quiet! This is what arose in machshava [i.e. thought]" (Menachot 29b) - that is to fix the defect.

So we find that all souls that are from the hand, through good deeds, are able to ascend to a very high level without limit, more than many other people who preceded them from earlier generations. Remember this.

Furthermore, even if a soul from the root of Cain comes into the world for the first time as a new soul, still he must rectify the blemish that occurred to his nefesh, ruach, and neshama from the sin of Cain - on the level of the portion of the root of which he is part.

Earlier we explained how positive and negative mitzvahs are dependent upon the 248 limbs of Adam’s soul, and how every limb includes flesh, tendons, and bones. The bones, the highest level, are on the level of the moach [bone-marrow] within them, and not on that of the bones themselves.

The...[tendons]...tie together all the limbs making them a single unit.

The next level down is the tendons, since a person's life-force runs through them, the blood moving through the arteries of the body. They also tie together all the limbs making them a single unit. The least of the three levels is the flesh.

On all three levels, flesh, tendons, and bones, there are souls which are considered to be the root of the level. They are the talmidei chachamim [Torah Scholars], ba’alei battim [householders], ba’alei ma’ase [doers of good deeds], and amei ha’Aretz" [simpletons]. This is true of all three levels in every limb.

There are long limbs, like the arms and thighs, within which there are large gaps between the souls. However, talmidei chachamim from the shoulder-limb and the like are very closely knit.

[Translation and commentary by Perets Auerbach.]