गोविन्द भाष्य (श्रील बलदेव विद्याभूषण - अचिन्त्यभेदाभेद वेदान्त ब्रह्मसूत्र भाष्य सटीक)

Siddhānta (conclusion): In the following words the author of the sūtras gives
the proper conclusion.
Sūtra 31
kartā śāstrārthavat-tvāt
kartā—the doer; śāstra—of the scriptures; ārtha—meaning; vat—possessing;
tvāt—because of having the nature.
He performs actions. This is so because the scriptures are meaningful.
Purport by Śrīla Baladeva Vidyābhūṣaṇa
It is the individual spirit soul who performs actions, not the modes of material
nature. Why is that? The sūtra explains: "Because the scriptures are meaningful."
In the scriptures it is said:
svarga-kāmo yajeta
"A person who desires Svargaloka should perform yajñas."
and
ātmānam eva lokam upāsīta
"One should worship the Supreme Personality of Godhead."
These statements have meaning only if the individual spirit soul does actually
perform actions. If all actions are performed by the modes of nature and the
individual spirit soul never does anything, these statements of the scriptures are
meaningless. These statements of scripture are intended to motivate the individual
spirit soul to act in a certain way so he can enjoy the results of his actions. It is not
even possible in this way to try to motivate the inert material modes to act in any
way at all.
That the individual spirit soul does actually perform actions is also confirmed
in the next sūtra.