The lessons we learn from the pilot actually greatly overlap with the lessons we learn from the prince because the pilot learns so much from the prince as well. Both teach the importance of spirituality, that things that are important in this world are the things unseen, the things connected to spirituality, such as love, trust, and faith. However, one thing we do learn first from the pilot, although the price reiterates the point later, is that what's on the outside is really just an unimportant shell.
The pilot first has this revelation when he and the prince go in search of a well in the desert. By the end of the chapter, the prince has fallen asleep while the pilot presses on. The pilot carries the sleeping boy in his arms. As he carries him he thinks to himself that he is carrying a "very fragile treasure" and admires the prince's external beauty, such as his "pale forehead" and his "locks of [golden] hair that trembled in the wind" (Ch. 24). However, the pilot says to himself that all of that physical beauty is really "nothing but a shell" and further states that "what is most important is invisible," which again ties back to the lessons learned throughout the book that the things of the spiritual world are what's truly valuable.
Therefore, two lessons we learn from the pilot in this chapter are that the things of the external world are really just empty shells, and that it's what's on the inside that is truly important.