A wealthy man had an only son and trusted him completely. In his later years he signed over the entire estate to the son's name, keeping nothing for himself except the promise of his son's care. The son agreed warmly, and at first treated his father with the love a father deserves.
Time passed. The son's attention drifted. He began to resent the old man at the table. He found his father's speech slow, his opinions outdated, his presence inconvenient. One by one the old man's comforts were taken away. His clean robes were replaced with simpler ones. His place at the table moved lower. Finally the son sent him out of the house altogether to live among the beggars at the town gate, while the son and his family kept the full estate for themselves.
One cold day the old man, in tattered clothing, met his own grandson playing near the gate. He asked the boy to go up to the house and beg his father for a mantle, since the cold was cutting him badly. The boy, wide-eyed and still innocent, ran home and passed on the request.
The father was annoyed, but he gave in. He told the boy to climb to the storage loft, find a particular mantle hanging on a hook, and bring it down. The boy went up. When he did not come back for a long time, the father climbed up to see what was delaying him.
The boy was carefully cutting the mantle in half with a knife.
"What on earth are you doing?" the father demanded.
The boy looked up without a trace of guile. "I am cutting the mantle in half. I will give Grandfather one half, and I am keeping the other half for when you are old."
The father stood speechless. In the innocent calculation of his own son, he read his whole future. The mantle he would earn one day by his own treatment of his father was already being reserved for him. He set down the knife, ran out to the town gate, and brought his father back home. He restored him to his full dignity and treated him with honor every day afterward (Gaster, Exempla No. 437).
The sages tell this parable to teach kibbud av va'em, the honor of father and mother, with an edge. Children learn by watching. The treatment a son shows his father is exactly the size of the mantle he is cutting for himself, and his own children are already taking note of the measurements.