Shaykh Yasir Qadhi divulges details on verses 77 to 79 that deal with the continuation on Musa and Khidr AS journey, the building of a wall by Khidr builds a wall, failure on the part of Musa to keep his part of the deal and an explanation by Khidr on why he punched a hole in the boat.
“So they twain departed; until, when they reached the people of a town. They asked its people for food, but they refused to make them guests. Then they found in it a wall about to fall, and he (Khidr) set it up. He (Musa) said: ‘If you had wished you could have taken a wage for it!’”“He (Khidr) said: ‘This is the separation between me and you. Now I will inform you of the interpretation of what you could not bear patiently’.”
“…He (Musa) said: ‘If you had wished you could have taken a wage for it!’”
Musa AS thought that the action of Khidr was not just that a person might sacrifice like that for a group of people who were so mean. It was at this exact time that the separation of the learned man and Musa AS took place due to inability of Musa AS to execute patience on his part as he had promised earlier.