Here is the foundational verse of the entire chapter. Krishna tells Arjuna: sattva, rajas, and tamas — these three gunas arise from Prakriti. And they bind the imperishable soul to the body.
Picture three ropes of different colours tied around a person. One is white — it binds through happiness and knowledge (sattva). One is red — it binds through desire and restless action (rajas). One is dark — it binds through ignorance and laziness (tamas). All three are ropes. Even the pleasant white one is still a binding.
Notice the paradox Krishna highlights. The soul is avyaya, imperishable and eternal. Yet these gunas keep it tethered to a mortal body. The binding is not real in the ultimate sense — it is a case of mistaken identity. The soul thinks it is the body and its qualities, and that misunderstanding is itself the chain.