B.G 18.18

ज्ञानं ज्ञेयं परिज्ञाता त्रिविधा कर्मचोदना। करणं कर्म कर्तेति त्रिविधः कर्मसङ्ग्रहः ॥१८॥

Knowledge, the object of knowledge, and the knower constitute the threefold impulse to action. Correspondingly, instrument, action, and the doer form the threefold aggregate of causes of actions.

Gīta Bhāshya 18.18

The term 'karma saṅgrahaḥ' in the context means 'collection of causes of actions'.
The hypothesis that recommended injunctions and moral rules have no effect on sentient beings because of the non-agency, similar to inert insentient things, is refuted. A sentient being differs from an insentient because of its intentionality (apekṣya), which arises from knowledge, the object of knowledge and the knower. Even in inaction, the egoistic sense of doership, i.e. intentionality is involved. Even when one is not the doer, desires arise by the grace of God, instrumented, based on the stated causes (knowledge, the object of knowledge, and the knower) through the method, and the benevolent human goal is achieved through actions.

एवं तर्हि न पुरुषं अपेक्ष्य विधिः। अकर्तृत्वात् इत्यत आह - ज्ञानं इति॥

Then, if it is postulated, that the rule does not dependent on a person due to non-agency, it is contradicted by the verse 'jñānaṃ', i.e. 'knowledge'.

त्रिविधा कर्मचोदना। एतत् त्रिविध मपेक्ष्य कर्मविधिः इति त्रिविधा उच्यते। कारणानि सङ्क्षिप्याह - करणं इति॥

The impulse to action is threefold (viz knowledge, the object of knowledge, and the knower). Considering this threefold impulse, the procedure of how action come about is described as threefold (instrument, action, and the doer). The causes (five types stated earlier) are summarized here as 'karaṇaṃ' i.e. the instrument.

कर्म सङ्ग्रहः कर्मकारणसङ्ग्रहः। अधिष्ठानादि करणे एव अन्तर्भूतः। तथाहि ऋग्वेदखिलेषु -

The term 'karma saṅgrahaḥ' in the context means 'collection of causes of actions'. Earlier indicated 'adhiṣṭhāna' i.e. body and others, are indeed included in the term 'instrument'. Hence, it is stated in Rigvedakhila:

"ज्ञानं ज्ञेयं ज्ञानिनं चाप्यपेक्ष्य विधिरुत्थितः। करणं चैव कर्ता च कर्मकारणसङ्ग्रहः॥"

"From 'knowledge, the knowable, and the knower' comes forth the intentionality governed by the methods and rules. The instrument and the doer are collectively the cause of actions."

इति।

- stated thus.

अकर्तृत्वेपि विधिद्वार ईश्वरप्रसादात् इच्छोत्पत्त्या उक्त कारणैः कर्मद्वारा पुरुषार्थो भवतीति। ईश्वराधीनत्वेपि विधिद्वारा नियतः तेनैव। यदि च इच्छादिः जायते तर्हि कारितमेव ईश्वरेण। फलं च नियतम्। वस्तुतो अकर्तृत्वेपि अभिमानिकं कर्तृत्वं तस्यैव। स्वातन्त्र्यं च जडमपेक्ष्येव इति न प्रवृत्तिविधि वैयर्थ्यम्। सर्वं चैतत् अनुभवोक्तप्रमाणसिद्धं इति न पृथक् प्रमाणमुच्यते ॥१८॥

Even when one is not the doer, desires arise by the grace of God, instrumented, based on the stated causes (Knowledge, the object of knowledge, and the knower) through the method, and the benevolent human goal is achieved through actions. These depend on God alone, operated by Him through the governing methods. If desires arise, then they are indeed caused by God. The results are also obtained through governing principles. In reality, even in non-doership, the egoistic sense of doership, i.e. intentionality, is involved which comes under His governance. Indeed, independence (of the sentient agent) is significant in comparison to the insentient due to its intentionality, and thus the injunction (to act) is not futile. All this is established by experiential evidence, and thus separate evidence is not required.

Gīta Tātparya 18.18

The term 'saṅgrahaḥ' refers collectively to the five causes. In the term 'karaṇa' i.e. instrument, the physical body is included. By the term 'daiva', the main agency of the God is indicated. By the term 'kartṛ' independent agency is indicated which is threefold. The term 'karma' i.e. action refers to 'ceṣṭā' i.e. various movements.
The Lord is the instigator of all beings' actions, and He alone is the inspiration behind the knower, known, and knowledge. This is because:
Speciality is twofold: one is called particular (how one is special) and the other is difference (how one is different from the other). Self-sufficiency of the Lord is not an indeterminate state, like the speciality of other ordinary entities, which are primarily based on difference. It is driven by the eternality of His innate-nature, which pervades everything. As His innate-nature is eternal, it becomes His speciality as well. (For a layperson, it is suffice to understand that the attributes of God are non-different from Him, because of His special properties, unlike other entities.)

"सम्प्रेरयितुरीशस्य कर्मस्वखिलचेतनान्। ज्ञातृज्ञेयज्ञानरूपा प्रेरणा सा स एव यत्॥

"The Lord is the instigator in all beings' actions, and He alone is the inspiration behind the knower, known, and knowledge.

स्वरूपेणैव नित्या सा विशेषात्मतया भवेत्। विशेषोऽपि स्वरूपेण नित्यश्च स्याद् विशेषतः॥

Because of the eternality of innate-nature, it becomes a special entity. As its innate-nature is eternal, that becomes its speciality.

स्वनिर्वाहकता यस्मात् नानवस्था विशिष्टवत्। विशेष्यस्य विशिष्टस्याप्यभेदेप्यविवादिनि॥

Self-sufficiency is not an indeterminate state, as it is like a particularity. Even in the non-difference, the speciality of particularity remains undisputed.

विशेषोऽस्त्येव नात्रास्ति हि अनवस्था कदाचन। ज्ञातुरन्योऽहमिति भेदस्तस्मात् तयोः कुतः। पश्यामीति विशेषोऽयमिदानीं मे समुत्थितः॥

Indeed, there is speciality and particularity here, as there is never any indeterminate state. Therefore, how can there be a confusion between 'I' the knower and another? 'I see,' - thus the particularity in me has now arisen.

इत्याद्यनुभवाद् भेदो न विशेष्यविशिष्टयोः। विशेषणं तु द्विविधं विशेषाख्यं तथेतरत्। विशेषमणयेद् येन प्रोक्तं तेन विशेषणम्। विशेषोऽपि विशेषस्य स्वस्यैव गमको भवेत्॥"

Thus, from the beginning of experience, there is no difference between the speciality and the particularity. Speciality is twofold: one is called particular, and the other is different. The speciality should lead by which it is said to be a qualification. The speciality should also be the indicator of itself."

इत्यादि तत्त्वविवेके।

- these are stated in the ancient text of Tattvavivek, i.e. the discrimination of principles.

सङ्ग्रहः पञ्चकारणानां सङ्क्षेपः। अधिष्ठानस्य करणे अन्तर्भावात्। दैवशब्दोदितेश्वरस्यैव मुख्यकर्तृत्वात् स्वतन्त्रकर्त्रोः कर्तृशब्देनैव उक्तेः त्रैविध्यम्। कर्म चेष्टा ॥१८॥

The term 'saṅgrahaḥ' refers collectively to the five causes. In the term 'karaṇa' i.e. instrument, the physical body is included. By the term 'daiva', the main agency of the God is indicated. By the term 'kartṛ' independent agency is indicated which is threefold. The term 'karma' i.e. action refers to 'ceṣṭā' i.e. various movements.