Yoga Sutras of Patanjali translated by Yogi Kalinath - Chapter 2, Verse 23
Pada 2, Sutra 23
Sva-svaami-shaktyoh svaroopopalabdhi-hetuh sanyogah
The correlation between the Seer and the seen is the cause for the apprehension of the essence and power of them both.
The Seer or Purusha is the Witness of the unfoldment of the seen or Nature/Prakriti. Nature allows us to make the distinction, by its variegation of activities, between the one that observes and what is being observed including our thoughts, emotions and feelings as these fluctuate just like the tides of Nature.
Anything that can be observed through our external (instruments of the body) and internal (instruments of the mind) senses is ephemeral, impermanent and in a state of flux. Proper use of the Buddhi or intelligence is to come to this realization and therefore develop a natural sense of detachment to anything that is ephemeral, impermanent and in a state of flux.
If one remains a Witness, i.e. becomes the Seer, the seen becomes the supporter of Moksha or Spiritual Emancipation.