The Three Gunas
Sattva, rajas, and tamas as the mechanism binding the embodied self — introduced in chapter 14, then applied to faith itself in chapter 17 and to renunciation in chapter 18.
BG 14.5
Harmony, Motion, Inertia, such are the qualities, Matter-born; they bind fast in the body, O great-armed one, the indestructible dweller in the body.
BG 14.19
When the Seer perceiveth no agent other than the qualities, and knoweth That which is higher than the qualities, he entereth into My Nature.
BG 14.26
And he who serveth Me exclusively by the Yoga of devotion, he, crossing beyond the qualities, he is fit to become the Eternal.
BG 17.2
Threefold is by nature the inborn faith of the embodied—pure, passionate, and dark. Hear thou of these.
BG 18.9
He who performeth a prescribed action, saying, "it ought to be done," O Arjuna, relinquishing attachment and also fruit, that relinquishment is regarded as pure.