There was once a certain rabbi who asked his students a question : how can we recognise the moment when night has ended and the day has begun?

The students thought deeply, pondering over the laws of sight and the phenomena of vision, and then, one by one offered their answers. One said that it was the moment when one could distinguish a white hair from a black hair when held in the palm of the hand. Another said, it is the moment when a shepherd looking into the field can tell a sheep from a dog. A third said, it is when, from a distance, we may know a fig tree from an olive. And a fourth, thinking of their studies, said, it is the moment when we can read the Torah without fear of error.

But after all had given their responses, the rabbi said, “No – it is this: when we see a stranger approaching, and we think he is our brother, that is the moment that night has ended, and the day has begun.”