"Bhikkhus, it is not easy to find a being who has not formerly been your mother...your father...your sister...your son...your daughter..."
If the above words of Buddha are true, then how can we be unkind to anyone? I came across this story while searching for some answers. Buddhism, though I am no Buddhist, is full of subtle powerful teachings that can be imbibed without following any rituals. I am in the stage of life where burdened by responsibilities, I might ignore my elders, parents, and in-laws, their advices, might find their habits irksome and might hurt them. This story teaches me filial piety. I understand now that we may have differences with people including our elders but that doesn't mean that we should stop being polite, kind, caring or dutiful towards them. And also that we can never repay the debt of kindness of our parents, all of them :)
Here is the abridged version of the story:
At one time, Buddha led a great assembly of bhikshus and boddhistavas on a walk toward the south. Suddenly they came upon a pile of bones beside the road. Buddha turned to face them, and bowed respectfully.
Ananda asked him in reverence, “What is the reason that the Great Teacher of the Triple Realm now bows to a pile of dried bones?
The Buddha told Ananda, "Although all of you are my foremost disciples, you still have not achieved far-reaching understanding. This pile of bones could have belonged to my ancestors from former lives. They could have been my parents in many past lives. That is the reason I now bow to them." The Buddha continued speaking to Ananda, "These bones we are looking at can be divided into two groups. One group is composed of the bones of men, which are heavy and white in color. The other group is composed of the bones of women, which are light and black in color."
Ananda said to the Buddha, "Once man and women die, all that is left are their bones. Please teach us how you are able to distinguish them."
The Buddha answered, "When men are in the world, they enter temples, listen to explanations of religious texts, make obeisance to the Triple Gem, and recite the Buddha's names, then when they die, their bones will be heavy and white in color. Most women in the world are saturated with emotion. They give birth to and raise children, feeling that this is their duty. Each child relies on its mother's milk for life and nourishment, and that milk is a transformation of the mother's blood. Each child can drink up to one thousand two hundred gallons of its mother's milk. Because of this drain on the mother's body whereby the child takes milk for its nourishment, the mother becomes worn and haggard and so her bones turn black in color and are light in weight."
And then the Buddha went on speaking about the kindness parents bestow over their growing children and how in return many children, on reaching adulthood, become ungrateful, defiant or hateful towards their parents and how such children suffer with horrible punishments in their afterlife.
At that time, upon hearing the Buddha speak about the depth of one's parent’s kindness, everyone in the Great Assembly threw themselves on the ground and began beating their breasts. Some fell unconscious to the ground, while others stamped their feet in grief. It was a long time before they could control themselves. With loud voices they lamented, "Such suffering! How painful! How painful! We are all offenders. We are criminals who have never awakened, like those who travel in a dark night. We have just now understood our offenses and our very insides are torn to bits. Please tell us how we can repay the deep kindness of our parents!"
The Tathagata used profoundly deep and pure sounds to speak to the assembly. "All of you should know this - If there were a person who carries his father on his left shoulder and his mother on his right shoulder until his bones were ground to powder by their weight as they bore through to the marrow, and if that person were to circumambulate Mount Sumeru for a hundred thousand kalpas until the blood that flowed out covered his ankles, that person would still not have repaid the deep kindness of his parents."
They reflected deeply, and said to the Buddha, "World Honored One, how can we repay the deep kindness of our parents?"
The Buddha replied, "Disciples of the Buddha, if you wish to repay your parents' kindness, repent of transgressions and offenses on their behalf. For the sake of your parents, make offerings to the Triple Gem. For the sake of your parents, hold the precept of pure eating. For the sake of your parents, practice giving and cultivate blessings. If you are able to do these things, you are being a filial child or else you are a person destined for the hells."
At that time, the Great Assembly, the gods, humans, asuras, and the others, hearing what the Buddha has said, were completely delighted. They believed the Buddha's teaching, received it, and offered up their conduct in accord with it.
All these teachings of the Buddha are recorded in a sutra called THE SUTRA ABOUT THE DEEP KINDNESS OF PARENTS AND THE DIFFICULTY OF REPAYING IT
Note: This is the abridged version of the story from here.