How does the soul control the intellect (buddhi)?

Question

Why does not the soul, that is so powerful, stop the intellect from choosing the wrong path/decision/karma?

How does the soul control the intellect (buddhi)?

Answer 1

The "soul" has different interpretations in different places and even in this site. Since you termed it as powerful than intellect, I am assuming that you mean "soul = Atma".

As per Gita, soul is beyond the intellect. Some may term "beyond" as "powerful". But that is one way of interpreting.

BG 3.42 — Senses are said to be beyond (to body), Mind is beyond Senses, Intellect is even beyond Mind, "That" is even beyond Intellect.
_{"That" -- may interpret Atma/soul}

Now on main Qn, "Why doesn't soul control the intellect?"

Because, soul is not the doer of anything, it's just an observer. Under the influence of the illusion/mAyA of prakruti, one may believe that 'I am the doer'.

BG 3.27 — All actions (karma-s) are enacted in Prakruti by [3] modes (guna-s). Bewildered with ego(false identity), the self(Atma) believes "'I' am the doer".
BG 5.8, 5.9 — "'I' certainly don't do anything" is believed by knower of fundamentals (tattva gyAna) - even while seeing, hearing, touching, smelling, eating, moving, dreaming, breathing, talking, discarding, accepting, opening, closing; -- "Senses only are acting in the subjects of senses" - is understood.

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Hence, from the "soul"'s perspective, there is neither right nor wrong. Neither choice nor indecisiveness, neither karma nor akarma. It's just a witness(sAkshi).

Performing right, wrong etc. is handled by the intellect(buddhi) only. Under the influence of sattva, the intellect makes the right decisions. This is clarified in further verses:

BG 18.30 — The one who knows activity & retirement, duty & non-duty, fear & boldness and bonding & liberation properly, has SAtvika Buddhi.
BG 18.31 — The one who doesn't know Dharma & Adharma, duty & non-duty as it is, has RAjasi Buddhi.
BG 18.32 — Covered by darkness (Tamas), the one who believes Adharma as Dharma and believes other [thing]s also wrongly, has TAmasi Buddhi.

But when the influence of sattva/rajas/tamas will be upon a person -- is unspecified. It's purely destiny.

Answer 2

Here is what Ramanujacharya has to say about it here.

I am now summarizing/paraphrasing the contents of the article here:

The soul is not just a "mute witness", but also a "doer/agent", because it has free will to make decisions, and reaps the good and bad rewards for its actions.

"This Purusa ever knows. He is indeed a seer, hearer, smeller, taster, thinker, knower, doer, a shiningātmā, a purusa" (Prasna Upanishad IV-9).

If the soul were merely a knower and not a doer, then it should not be responsible for its actions, yet it is. Also, this would imply complete determinism and Shastras, which prescribe instructions and dharma, would be useless.

However, the soul being pure consciousness and a knower, cannot do anything by itself, so it needs a material body as an instrument to carry out actions. But because it became deluded by Maya and thought it was the body itself, it thus became under the influence of the 3 gunas and thought that itself was the doer and not Prakriti being used as an instrument.

Insentient matter cannot be a "doer" but merely a "compeller", it influences the soul to act in a particular way. So a person with Tamas guna will be inclined to sleep. However, the decision to sleep or not is up to the soul, and the soul can also make the decision to become Sattvik.

However, one who realizes he is Atma and not Prakriti, is not controlled by Prakriti, but becomes the controller of it.