Bhai Amar Das ji had just performed a miracle which was not pleasing to the Guru, but he had apologized and the Guru forgave him. On their way back to Khadur, the Guru's home, the Guru and his companions stayed with a devotee who had asked the Guru to bless his soul by visiting his house.
When they had returned to Khadur, Bhai Amar Das continued to serve the Guru with all his heart.
The Guru replied: "The saints of the True Guru are like clouds. They take a body to help the world and bless people. The body is a vessel which will always die. A rich man drops old torn clothes to put on new ones. A saint drops the aging body when it has done its service. Death is nothing but changing one's clothes."
Many times he almost slipped but... as if the angels were helping him, he continued on his errand without falling. When he finally reached the river he found that if he filled the pot to the brim, it was too heavy to lift out of the river.
So he got in the river with the pot on his head and submerged himself completely in the water to put the pot on his head under the wayer. He got out dripping wet with the full pot of water on his head. In the dark night there was no way to find the right way back. He came upon the weavers house. Next to the house there were holes in the ground the weavers used to steady their looms. Bhai Amar Das tripped in one of the holes and fell down hard. Without concern for himself he did his best to make sure the water didn't spill. Somehow, he managed to not spill the pot of water.
Bhai Amar Das showed his patience and didn't mind that she had slandered him.
"SatiNam" he said. "And what kind of Guru would make a 73 year old man do a fools errand in a dark storm like this!?" she replied.
Then he continued onward to bring the water to the Guru. He ventured through the muddy, cold, wet darkness and finally reached the Guru's house. He had passed his final test of devotion. The Guru joyously hugged Bhai Amar Das ji The next Guru had been chosen.
Everything Guru Angad said came true. Guru Angad called for a ceremony and announced that Amar Das would sit on the throne of Nanak.
"My sons, bow to Amar Das. All my beloved Sikhs, Amar Das is the True Guru. Whoever will serve him will be happy in this world and exalted in the next world. Whoever will be jealous of him will be sad." Soon after that, Guru Angad left his physical body and Guru Amar Das stood as savior for the people of this world in this dark age.