Hakim al Umma Mawlana Ashraf Ali Thanawi (Allah have mercy on him) has mentioned the following lessons that can be learned from the story of our masters Prophet Musa  and Khidhir (Allah’s peace be upon them):

1. Desirability of travel for a student (to pursue his learning).
2. To have respect (adab) when dealing with scholars and shuyuk.
3. To abandon criticism of scholars and shuyuk
4. To find an excuse for their apparently unclear actions, dealings and speech.
5. To fulfill the pact (ahed) made with them.
6. To apologize for any thing committed against them.
7. To keep provision for the way while traveling. It is not against tawakul (reliance on
Allah)to do so.
8. To ascribe forgetfulness and other disliked things to Shaytan. It is from adab not to
attribute them to Allah.
9. For a scholar to refuse teaching a subject to a student whom he thinks is incapable of
understanding it.
10. To give preference to Allah’s command in every thing.
11. For a guide to put some essential criteria to be fulfilled, for his followers.
12. To condone forgetfulness.
13. Three attempts to be sufficient enough to be counted as repetition.
14. Boat ride to be permissible.
15. The ruling to be on the evident matters. Until one comes to know the reality.
16. Asking for food to be permissible, in case of absolute necessity.
17. Not to give up chivalry. Even if it is for those who do not deserve it.
18. To take monetary retribution for worldly tasks done.
19. The condition for being in need to persist even if tools for earning or possession of
insufficient funds exist.
20. Being angry (that is displaying it) is impermissible (haraam).
21. Hiding wealth by burying it in the ground (for protection) to be permissible

And many more lessons can be learned.

Hakim al Umma adds; this incident proves that the best way for islah (reformation) is through physical demonstration (actions) not merely by (admonition via) speech.

Masail us sulook, pages 328-9