B.G 18.18

jñānaṃ jñeyaṃ parijñātā trividhā karmacodanā। karaṇaṃ karma karteti trividhaḥ karmasaṅgrahaḥ ॥18॥

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.

evaṃ tarhi na puruṣaṃ apekṣya vidhiḥ। akartṛtvāt ityata āha - jñānaṃ iti॥

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'.

trividhā karmacodanā। etat trividh mapekṣya karmavidhiḥ iti trividhā ucyate। kāraṇāni saṅkṣipyāha - karaṇaṃ iti॥

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.

karma saṅgrahaḥ karmakāraṇasaṅgrahaḥ। adhiṣṭhānādi karaṇe eva antarbhūtaḥ। tathāhi ṛgvedakhileṣu -

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:

"jñānaṃ jñeyaṃ jñāninaṃ cāpyapekṣya vidhirutthitaḥ। karaṇaṃ caiva kartā ca karmakāraṇasaṅgrahaḥ॥"

"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."

iti।

- stated thus.

akartṛtve'pi vidhidvāra īśvaraprasādāt icchotpattayā ukta kāraṇaiḥ karmadvārā puruṣārtho bhavatīti। īśvarādhīnatve'pi vidhidvārā niyataḥ tenaiva। yadi ca icchādiḥ jāyate tarhi kāritameva īśvareṇa। phalaṃ ca niyatam। vastuto akartṛtve'pi abhimānikaṃ kartṛtvaṃ tasyaiva। svātantryaṃ ca jaḍamapekṣyeva iti na pravṛttividhi vaiyarthyām। sarvaṃ caitat anubhavoktapramāṇasiddhaṃ iti na pṛthak pramāṇamucyate ॥18॥

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.)

"samprerayiturīśasya karmasvakhilacetanān। jñātṛjñeyajñānarūpā preranā sā sa eva yat॥

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

svarūpeṇaiva nityā sā viśeṣātmatayā bhavet। viśeṣo'pi svarūpeṇa nityaśca syād viśeṣataḥ॥

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

svanirvāhakatā yasmāt nānavasthā viśiṣṭavat। viśeṣyasya viśiṣṭasyāpyabhedepyavivādini॥

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

viśeṣo'styeva nātrāsti hi anavasthā kadācana। jñāturanyo'hamiti bhedastasmāt tayoḥ kutaḥ। paśyāmīti viśeṣo'yamidānīṃ me samutthitaḥ॥

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.

ityādyanubhavād bhedo na viśeṣyaviśiṣṭayoḥ। viśeṣaṇaṃ tu dvividhaṃ viśeṣākhyaṃ tathetarat। viśeṣamaṇayed yena proktaṃ tena viśeṣaṇam। viśeṣo'pi viśeṣasya svasyaiva gamako bhavet॥"

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."

ityādi tattvaviveke।

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

saṅgrahaḥ pañcakāraṇānāṃ saṅkṣepaḥ। adhiṣṭhānasya karaṇe antarbhāvāt। daivaśabdoditeśvarasyaiva mukhyakartṛtvāt svatantrakartroḥ kartṛśabdenaiva ukteḥ traividhyam। karma ceṣṭā ॥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.