In fact, by all rights the soul should actually and quite naturally purify
the body to a truly supernatural degree when an individual is born, whether
he’s worthy of that or not, given how inherently pure the soul is.
But the point is that G-d purposefully disallowed for that 1, and
keeps the soul at bay, if you will, in the course of one’s life, so that His
intentions 2 can be fulfilled. So the soul does what it does
while it is in the body, and no more, where it otherwise sits stifled and
withdrawn, so to speak 3.
It’s also true that the soul should likewise be able to expand and irradiate
as the individual engages in good deeds in his life, and to purify the body
then to a degree. But that, too, was denied the soul in life.
But those restraints will all be removed in the course of the Resurrection
of the Dead, when the soul will purify the body in one fell swoop
4. And the combination of body and soul will grow higher and
higher 5 to the degree that accords with the sort of person that
individual had come to be in life 6, until they become worthy of
the World to Come where they can continue to grow 7.
1. Because of Adam and Eve’s sin.
2. That humans be subject to free will.
3. And it “expresses itself” to a degree in The Soul World as we said in
1:3:11-12. Also see 1:4:2 below and Da’at Tevunot 72.
4. Also see Da’at Tevunot 72, 146-148.
5. See Berachot 17a; Zohar 2:83a, 1:135b; Sha’ar HaGemul.
6. See the end of Ch. I of Messilat Yesharim.
7. Thus it’s written that “Sages have no rest, neither in this world nor
in the next” (Berachot 64a). See Emunot v’De’ot 9:10.
See Klallim Rishonim 23 for a laying out of what will happen to
the body and soul step by step in the course of the 7th, 8th, 9th, and 10th
Rabbi Yaakov Feldman has translated and commented upon "The Gates of Repentance", "The Path of the Just", and "The Duties of the Heart" (Jason
Aronson Publishers). His works are available in bookstores and in various
locations on the Web.