One could say that the narrator learns many significant lessons from his brother such as perseverance, faith, and unconditional love. He also learned about the vast spectrum of human emotions from guilt and jealousy to grief, pride, accomplishment, and so on.
Doodle's brother may not have recognized the importance Doodle played in his life until he was an adult, which is why he is telling his story now. He uses his younger perspective to share the story, and this illustrates the immense amount of guilt he feels about the way that he treated his brother when he was younger as well as the responsibility he feels in his brother's death. However, the narrator's actions as Doodle's brother were perfectly normal for a child.
Obviously one who reads the story must understand this perspective. As a child, he could not process the enormity of Doodle's condition nor did he understand Doddle's limitations or his family's feelings and expectations. This story solely focuses on his experiences as a child and coming to terms with those memories as an adult.
"The Scarlet Ibis" employs the retrospective point of view. The adult narrator looks back and tells the story of his relationship with Doodle and how Doodle died. As an adult, the narrator now understands Doodle and himself much more fully, and he now recognizes how his own selfish pride led to Doodle's tragic death. The fact that he is still thinking about events that happened years before during his childhood suggests that he is still attempting to understand them and come to terms with who he had been as a child and what he had done.
The narrator's memories of Doodle suggest that he learned many profound lessons from his little brother, lessons he didn't recognize or appreciate until years later. He learned about unconditional love and loyalty, because Doodle loved him always, even when the narrator was treating Doodle with deliberate cruelty. He learned about gentleness and sensitivity. (He remembered watching Doodle struggle alone to bury the ibis.) Most importantly, he learned lessons about real courage by watching Doodle fight to survive from the time he was born and then, as he grew up, struggle against his physical limitations in order to please his big brother. Finally, the narrator learned, too late, that Doodle was a rare and beautiful spirit who was unappreciated by his family.