Like many of Salinger's works, "Teddy" glorifies a young child as pure and beautiful at the expense of seemingly crass, jaded, and materialistic adults. The author grants this particular child, Teddy McArdle, with the spiritual wisdom of many lifetimes (Teddy believes in reincarnation) and intelligence far beyond his years. Because Teddy is a child, many of the adults around him miss the value of his insights.
"Teddy" employs the typical Salinger dichotomy between ignorant adults and wise children.
Nicholson is unable to learn from Teddy because he can't get past Teddy's age.