Darn huge question, brother!

 For me, as I see it it was an opportunity to wean his family from his personal presence lessening their dependence on him. More importantly, as I remember the instructions and counsel given by Immanuel before Michael left to become Jesus was that he was to meet as many people of the time every where, as many of his children to get to know what each of them were like in their different lives. 

It was also to plant the seeds for the future missions of his messengers in bringing the gospel in those areas and beyond. 

What he learned about mankind? Difficult to answer. Mankind means ALL of humanity...really too general. What do you think he learned? That everyone of his children was /is unique; some are truth-seekers, some not...etc etc etc...need to read. But he learned what you and I learn about people...everyone is different! 

He learnt that he was soon to start his life work of becoming a spiritual teacher upon his return to his land. 

Hope this helps! Sorry, so late...was away. 

Monica