Purport

As we see everywhere that people differentiate among fellow humans on different grounds. Sometimes based on wealth, some other time based on class and yet at other times based upon even the skin color. That is a clear fault.
In above Shloka Bhagwan Shri Krishna establishes beyond doubts that every not only human but every living being should be treated with equality. Different living beings may have varied shapes and sizes, some living being appears superior, more beautiful or powerful than others, but at the level of soul, no such differentiation exists. Only differentiation exist is that of Karma.

At other places, Bhagwan make this clear
"A true yogī observes Me in all beings, and also sees every being in Me. Indeed, the self-realized man sees Me everywhere.." --(Ch6: Sh29)

Bhagwan says a person who treats all living beings with equality is the real wise one. Anybody who differentiates between a human on any ground is certainly at fault.
This is just one of the Shlokas, among dozens of others where Bhagwan Shri Krishna instruct us human to treat not just human but all living being with equality.