Bhagavad Gita Verse 18, Chapter 5

vidyavinayasampanne braamhane gavi hastini |
shuni chaiva shvapaake cha panditaaha samadarshinaha || 18 ||
 
A braahman endowed with knowledge and sense control, a cow, an elephant, a dog, even a dog-eater - the wise person perceives (all these) as one.
 
vidya : knowledge
vinaya : sense controlled
sampanne : endowed with
braamhane : a braahman
gavi : a cow
hastini : an elephant
shuni : a dog
cha : and
eva : even
shvapaake : dog-eater
cha : and
panditaaha : wise person
samadarshinaha : perceives as one
 
Shri Krishna further elaborates on the vision of a realized seeker in this shloka. Unlike most of us how tend to focus on the differences, the realized seeker focuses on the eternal essence which is common in every plant, animal, human, situation and inanimate object. In chapter two, we saw the example of the child who wants a cookie shaped like a lion, whereas the adult does not really care because his focus is in the dough that is common within each cookie.
 
A spectrum of entities has been laid out before us, from the braahman that has a high level of sattva, to a cow that has lesser sattvic content, all the way to an individual with a miniscule, almost non-existent level of sattva. Shri Krishna says that the wise person sees the eternal essence in all of them.
 
This ability to see the oneness is all is praised throughout our scriptures. In the Raamaayana, Tulsidaas says the one should view both friends and enemies equally. Why? Because when enemies leave, they give sorrow. But when friends leave, they too give sorrow. It is just a matter of perspective.
 
Now, just because the wise person views everyone with a similar vision does not mean he treats them similarly, or deals with them similarly. He will deal with a dog differently than how he would treat a braahman. How is it possible? It is just like we see our body as one, but we treat our eye differently then we would treat the soles of our feet.
 
Footnotes
 
1. "Vinaya" usually means humility, but it is translated as sense control in the context of this shloka.