Once, the Bodhisattva or the Enlightened Being was born into an ordinary family. In his next 500 births, he had the same father. Then the father was his uncle for another 500 births and then grandfather for the next 500 births. The Bodhisattva had the same mother for the next 500 births, who had been then his aunt for the next 500 births. She was then reborn as his grandmother for another 500 births. After 3,000 births, the man and the woman who had 1,500 births then became husband and wife. This time the Bodhisattva had a different father and mother. However, as he was the Enlightened Being, he respected not only his own mother and father, but also his parents from previous births.
Moral: Be respectful and kind to all. All of us are related some way or the other.