Text 20 

sarva-bhutesu yenaikam
bhavam avyayam iksate
avibhaktam vibhaktesu
taj jnanam viddhi sattvikam

Translation

That knowledge by which one undivided spiritual nature is seen in all living entities, though they are divided into innumerable forms, you should understand to be in the mode of goodness.

Commentary by Srila Prabhupada 

A person who sees one spirit soul in every living being, whether a demigod, human being, animal, bird, beast, aquatic or plant, possesses knowledge in the mode of goodness. In all living entities, one spirit soul is there, although they have different bodies in terms of their previous work. As described in the Seventh Chapter, the manifestation of the living force in every body is due to the superior nature of the Supreme Lord. Thus to see that one superior nature, that living force, in every body is to see in the mode of goodness. That living energy is imperishable, although the bodies are perishable. Differences are perceived in terms of the body; because there are many forms of material existence in conditional life, the living force appears to be divided. Such impersonal knowledge is an aspect of self-realization.

Commentary by Sri Visvanatha Cakravarti Thakur

This verse speaks of sattvika process of knowing. Seeing one soul (ekam bhavam), with one form (avibhaktam) which is indestructible (avyayam) residing one by one in different forms (vibhaktesu) such as human, devata, or animal for the purpose of enjoying various fruits, which are temporary, through knowledge related to action (verse 18), is known as sattvika knowledge.