Eddie as a ghost
Eddie's legacy haunts the boy who wants to know the truth and proclaim it. His family stands against him, protecting their secrets from him, telling him to stop trying to figure things out. In other words, Eddie represents a real haunting for the boy who becomes obsessed with defending his legacy.
The boy as "poet"
This novel was written by an Irish poet, which helps explain why the boy isn't named. Perhaps this is like writing a poem not from one's own point of view, but from the point of view of an abstract "poet." In other words, the boy's namelessness represents the fact that he represents a point of view that many share. He represents the tenuous relationship between Irish citizens and the IRA.
The IRA's mistake
By saying that the IRA wrongly executed his uncle, the boy is parting ways with those who silently support them in their (often terroristic) ways. His uncle's execution is an act of terrorism, because it was done to make Eddie an example for what happens to informants. The fact that they made a mistake and executed Eddie instead of McIlhenny serves as a symbolic reminder that the IRA is not just.
The escape to America
By observing that the real snitch, McIlhenny, got away from the police and the IRA to live in America, he makes a symbol. McIlhenny is a reminder that many are so threatened by the reign of the IRA in Ireland that they are forced to move as refugees of war, essentially. It is insightful that the true culprit also moved to America, a symbol for the departure from national pride (which the IRA views as intolerable).
The novel as allegory
There are a number or reasons to suggest that this short novel is actually an allegory. There are literary suggestions, like the unnamed narrator (which lends a broader scope to the arguments of the story) and also the allegorical implications of Eddie's wrongful death and the boy's maturing journey toward truth and independence. As an allegory, it implies that we often have to be willing to distrust our family, friends, and culture, in order to distance ourselves from the temptation to join in their group think. The boy experiences this most powerfully when he separates himself from his mother's religious superstitions (also a broader symbol, perhaps as the poet's subtle argument that Irish Christianity needs a reboot).
