In the moonlight I looked at his pale forehead, his closed eyes, his locks of hair that trembled in the wind, and I said to myself: "What I see here is nothing but a shell. What is most important is invisible.”
 

One of the most crucial lessons in The Little Prince is that the essential things in life are invisible to the eye. In this passage, the invisible thing being referenced is the soul. The narrator realizes that the entirety of the little prince’s personhood and being cannot be captured simply by his physical body. His essence, or his soul, is a nonvisible thing, yet it is what makes the little prince alive and unique. The little prince’s body is simply a shell in which his soul resides. It’s pivotal that the narrator realizes this truth, as the little prince is about to depart from Earth, leaving his body behind in the process. To a human being, this process looks remarkably like death. But the idea that the little prince’s body is not truly him, and that his essence or soul might live on, returned finally to its home, gives the narrator hope and comfort amid his grief.

I remembered the fox. One runs the risk of weeping a little, if one lets himself be tamed.

The narrator has heard the little prince’s story of how he tamed the fox. Now knowing that to be tamed means to become emotionally bonded with another living being, he realizes that he has been tamed by the little prince. Their emotional connection means that the little prince’s departure will be especially hard for the narrator, who will be forced to say goodbye to someone he loves. The narrator realizes that loving someone often comes with pain and grief.

Children should always show great forbearance toward grown-up people.

In The Little Prince, the narrator often remarks that adults have lost their ability to see essential truths, to use their imaginations, and to live in a fulfilling way, while children often innately understand these things. This line is a humorous switching of our normalized hierarchy, in which children are naive and silly, while adults are wise and knowledgeable. In the world of The Little Prince, children are the wise ones, and the narrator advises that children remain patient when dealing with grown-ups and their lack of understanding.