Excerpt from Bhagavad Gita, In the Light of Kashmir Shaivism, by Swami Lakshmanjoo, chapter 18.
From the 26th śloka, there is [explanation of] kartā, which means the doer: sāttvic doer, rājas doer, and tāmas doer.
muktasaṅgo’nahaṁvādī dhṛtyutsāhasamanvitaḥ /
siddhyasiddhyornirvikāraḥ kartā sāttvika ucyate //26//
Muktasaṅga, who is not attached to whatever action he does, he is not attached to it. Anahaṁ vādī, and he does not believe that, “I have done this” [or] “I am doing this.” Dhṛti utsāha samanvitaḥ, he has got courage, he has got tolerance and courage. He does his work with tolerance and courage. And he is not moved if that work is fulfilled or if that work remains unfulfilled. In these both ways, he remains the same. And this way of doer is called sāttvic doer. And he is on the right path; this way of doing is the right way of doing.
rāgī karmaphalaprepsurlubdho hiṁsātmako’śuciḥ /
harṣaśokānvitaḥ kartā rājasaḥ parikīrtyate //27//
[The rājas doer is] rāgī, who has got attachment for that work; karma phala-prepsur, who always craves and longs for its fruit; lubdho, he has too much greed; hiṁsātmaka, he does not mind if somebody is harmed by [his] doing. [He feels], “let him be harmed. I must get its fruit.” Aśuciḥ, and his behavior is dirty [i.e., impure]; harṣaśokānvitaḥ, he is always with harṣa means happiness and śoka is grief; happiness and grief are absolutely at his disposal. If he has done... if he is successful in his doing [something], he is happy; if he is not successful, he is filled with grief. This way of doer is called rājas doer and it has no value.
Now the doer of action in tāmasa state.
ayuktaḥ prākṛtaḥ stabdhaḥ śaṭho naikṛtiko’lasaḥ /
viṣādī dīrghasūtraśca kartā tāmasa ucyate //28//
Ayuktaḥ, who does not know how to do this action [and] who is not truly doing actions with good behavior. Prākṛtaḥ, he does not listen to anybody’s suggestion that, “this way you should do it.” [He replies], “no, no, no, I don’t like your suggestion, I know how to do it.” That is prākṛtaḥ, he depends upon his own [limited] understanding. Stabdhaḥ (stabdhaḥ means he is unmoved by others suggestions). Śaṭha, he is śaṭha (śaṭha means he is internally rigid). Naikṛtika (naikṛtika [means] he has no compassion for others). Alasaḥ (alasaḥ means he is always sluggish). Viṣādī, he is always repenting [afterwards], “I have done it wrongly." Dīrgha sūtraśca, and his [activity] takes more [time] than anything in this world, more time. [If] he can do that work of half an hour, it will take him at least fifteen days to complete it. This way of doer is called tāmas doer.