The rabbi asked his students: "How can we determine the hour of dawn, when the night ends and the day begins?
One of the rabbi's students suggested: "When from a distance you can distinguish between a dog and a sheep?"
"No," was the answer of the rabbi.
"Is it when one can distinguish between a fig tree and a grapevine?" asked a second student.
"No," the rabbi said.
"Please tell us the answer then," said the students.
"It is, then," said the wise teacher , "when you can look into the face of another human being and you have enough light in you to recognise your brother or your sister. Until then, it is night, and darkness is still with us."
Source: Finding My Way Home (Henri J.M. Nouwen)