"Nothing Gold Can Stay" is a poem by Robert Frost. Ponyboy learned this poem in English class. He remembers it when he is watching the sunrise with Johnny, while they are hiding out in the church in Windrixville. He recites the poem, but feels as though he is missing the meaning.
Later on, after Johnny tells Ponyboy to "stay gold", Ponyboy finds the meaning in the poem. The poem reflects the boys' loss of innocence in their harrowing experiences as Greasers. After the murder, the boys are irrevocably changed. Ponyboy realizes that Johnny wants Ponyboy to continue to see the good in the world. In Johnny's letter to Pony, he expresses that he believes that though he knows he will die from his injuries, it was worth it to save the innocent children. He is seeing the good.
In "Nothing Gold Can Stay", the speaker refers to Eden, or the biblical loss of innocence. When Pony grasps this meaning, he decides to write his theme for English class, which is the story told in the novel. Pony is thinking of all the young men he knows who have suffered and have been deprived of seeing the good, the innocence, or the "gold" in the world. Through his writing, he hopes to change that.
Nothing good can stay one day you will turn bad.