Verse 19: What does Spirit do?

tasmāt-ca viparyāsāt siddhaṃ sākṣitvam-asya puruṣasya |
kaivalyaṃ mādhyastyaṃ draṣṭṛtvam-akartṛbhāvaḥ ca ||

sākṣitva – witness
kaivalya – independent/separate
madhya – impartial
draṣṭṛ – seer
akartṛ – not an agent

Nothing. Spirit is an isolated and inactive witness.

1. Spirit (Purusa) is that which is without the three Gunas.
2. The absence of the three Gunas implies a solitary/isolated Spirit. It never changes or combines with anything else.
3. The three Gunas are the source of all action. Therefore, the absence of the Gunas makes spirit a non-agent. It can’t do anything.
4. The absence of the three Gunas and the inability to act also makes Spirit indifferent to the effects of the three Gunas: pleasure, pain and delusion.
5. Spirit is however sentient/conscious which makes it a seer.
6. Spirit is a witness. Objects are not shown to other objects. Objects are shown to a witness. The Unmanifest (Prakrti) presents its creations to Spirit.