sarvabhooteshu yenaikam bhaavamavyayameekshate |
avibhaktam vibhakteshu tajjnyaanam viddhi saattvikam || 20 ||

By which one sees a single, imperishable, indivisible entity in all diverse beings, know that knowledge to be sattvic.
sarvabhooteshu : in all beings
yena : by which
ekam : single
bhaavam : entity
avyayam : imperishable
eekshate : one sees
avibhaktam : indivisible
vibhakteshu : diverse
tat : that
jnyaanam :knowledge
viddhi : know
saattvikam : saattvic
Knowledge, the doer and action were introduced in the prior shloka. Shri Krishna now begins the analysis of knowledge. To recap, jnyaanam or knowledge here refers to the meaning given by an individual to information conveyed by the senses and the mind. The view of a large garden, for instance, could be interpreted differently by different people. A nature lover would rush towards it. A city dweller may think of it is a waste of living space. A real estate developer would imagine a resort being built on it, and all the consequent profits that follow from it.
Knowledge can be saattvic, raajasic or taamasic, since it is a product of Prakriti or nature. Sattvic knowledge is taken up here. The mind and the senses, by their very nature, report a diverse world. Shri Krishna says that the vision that can see unity within this diversity is called saattvic vision or knowledge. Few people have such a vision, since it is hard to fight against the normal tendency of the mind to chop up the world into fragments. Only someone with a saattvic vision like Mahatma Gandhi, for instance, could rally diverse and antagonistic states towards the idea of a united Indian nation.
Ultimately, a sattvic vision of seeing unity in diversity paves the way to understanding that the entire universe is pervaded by one single, imperishable, undivided entity. Initially, this entity is the eternal essence with attributes, the saguna brahman, also known as Ishvara. At the conclusion of the spiritual journey, the understanding evolves to recognize this entity as the nirguna brahman, the pure eternal essence, which is our own self. We can develop such a unified vision, this samyak darshana, through karma yoga. Instead of serving ourselves, we serve our family, then our community, our company, our state, our nation and eventually, Ishvara.