A rabbi asked his students, When is it at dawn that one can tell the light from the darkness?

One student replied, When I can tell a goat from a donkey.
No, answered the rabbi.
Another said, When I can tell a palm tree from a fig.
No, answered the rabbi again.
Well, then what is the answer? His students pressed him.

Only when you look into the face of every man and every woman and see your brother and your sister, said the rabbi.
Only then have you seen the light. All else is still darkness.