Adi Sankara’s pithru bhakthi brings divine grace
Sankara knew the real meaning of the Vedic words ‘Matru Devo Bhava, Pitru Devo Bhava.’ ( May your mother be your God , may your father be your God.)
Once when his father left the house, he told his son: “My dear son, I am daily worshipping God and distributing naivedya ( edible items offered to God) to all the people . So also in my absence and in the absence of your mother , you will please do like that.” Sankara promised to do so without fail.
He poured some milk in a cup, put it before the Idol of the goddess and prayed to her : mother ! Take this milk which I am offering.”Though he prayed for a long time, She did not appear . He was very much disappointed. He said again,” Mother! You are not accepting the offering which I am giving to you.? “He prayed to her earnestly from the innermost depths of his heart. 
He was prepared to sacrifice even his life and told himself, “my father asked me to offer this milk to the Goddess but I am not able to do so because the Goddess is not receiving the offering which I made. It is better that I die.” He went out and brought a big stone to kill himself.
The Mother of the universe is very compassionate and she was very much moved and touched by Sankara’s sincerity. She at once appeared before him and drank the milk that he offered. She drank the whole milk and placed the empty cup before him. The boy was very glad that the mother of the universe came and drank the milk but there was nothing in three cup to distribute to others. He thought that his father would certainly ask for the naivedya of the God after his return. He feared that the father may think that he drank all the milk and may be angry with him. Therefore he again prayed to the Goddess , “Goddess; give me at least a drop of milk so that I may be able to give it to my father.” But the Goddess did not come.
He again sincerely continued to pray. The Goddess was moved and She again appeared. Because She was not able to give the milk that She drank, She gave Her own milk and filled the cup. There is a belief that because Sankara tasted the Divine milk, he was able to attain the highest learning, knowledge and wisdom that is ever possible. So the essence of the grace of the Goddess became the essence of the learning of Sankara. In order to please his father, he tried hard and was able to get the Goddess of the Universe to manifest Herself before him. From this story , we must learn to revere and obey the orders of our fathers implicitly and sincerely.