There are a number of themes at work in James Baldwin's novel, Go Tell It on the Mountain. This is a novel about family and personal history, about identity and about coming of age. These three elements of the novel overlap a great deal, but they can each be discussed as distinct themes in the work.
Perhaps the most often discussed theme of Baldwin's novel is that of "coming of age." Over the course of the narrative, John develops from a child (in the eyes of his church/community) into a young man. In confronting his father (although obliquely) John makes a claim to self-ownership.
In his experience of being saved, John establishes a personal relationship with Jesus. This is a very important, highly formalized moment and it stands as a significant step in John's maturity - especially in the context of the church. (We should note when discussing John's spiritual epiphany that by establishing a personal relationship with Christ, John no longer needs to rely on the mediation or guidance of his father in this area.)
The "coming of age" elements of Go Tell It on the Mountain are closely linked to the novel's central interest in identity.
"Go Tell It on the Mountain is primarily about John Grimes' quest to find out who he really is, to distinguish the values of those around him from the ones that he holds" (eNotes).
This theme relates most strongly to John, the protagonist of the novel, but can also be seen in relation to all the principal characters of the narrative (John, Gabriel, Elizabeth and Florence). One could certainly argue that the novel, on the whole, presents an answer to a hypothetical question from John - "Who am I now and who am I going to be?"
In narrating the histories of John's family, Baldwin's novel also examines how experience shapes personalities and how family ties can have powerful (and sometimes overwhelming) effects on an individual's personal development.
When we reach the end of the novel, John's story of personal maturity has been told.
"For he had made his decision. He would not be like his father, or his father's fathers. He would have another life” (Baldwin).
He has grown up, distanced himself from his father and taken big steps toward an adulthood where he will choose to define himself (as much as that is possible). The stories of his family have also been told. These stories all emphasize the notion of identity as a product of personal history and of circumstances.