As Grant waits to hear about Jefferson's execution what appears as a sign that he can say goodbye?
The ending image of Grant seeing the butterfly is the sign for him to recognize that the execution has ended and that he can say goodbye. At this particular point in the narrative, Grant is not with Jefferson at the execution. He is at his school. Yet, his mind wanders to what the execution must be like. It is at this moment that Grant's mind begins to reflect openly about the execution and what it means.
Part of this rumination is centered on the field that Grant walks upon while he waits for word of the execution. Another part is based on Grant's own guilt for not being there at Jefferson's final moments: "Why wasn't I there? Why wasn't I standing beside him? Why wasn't my arm around him? Why? Why wasn't I back there with the children? Why wasn't down on my knees? Why?" These questions continue as Jefferson ponders the nature of the divine in the midst of such human suffering: " Don't tell me to believe. Don't tell me to believe in the same God or laws that men believe in who commit these murders. Don't tell me to believe that God can bless this country and that men are judged by their peers." In the midst of this emotional intensity, Grant sees a butterfly and his thinking pivots into a new direction, one where some notion of unity is brought about from the darkness of questions that cannot be definitively answered. Grant notices the butterfly, wondering why it chose to sit there, next to him when it had other areas to rest. Grant recognizes the unity of the moment that the butterfly brings with it:
I watched it closely, the way it opened its wings and closed them, the way it opened its wings again, fluttered, closed its wings for a second or two, then opened them again and flew away. I watched it fly over the ditch and down into the quarter, I watched it until I could not see it. Yes, I told myself. It is finally over.
This becomes the instant when Grant is able to say farewell to Jefferson. Given how emotionally tattered Grant is, it is the closest thing to him being able to say goodbye to Jefferson. It is not direct, but it is symbolic. It is a moment in which Grant is able to recognize the finality of the moment. The butterfly's opening of wings and ability to fly away is what enables Grant to say goodbye to Jefferson. The butterfly is a symbol that enables some semblance of emotional unity to present itself in a situation where there is little in way of harmony. This is accentuated with Paul's extension of friendship to Grant at the end, something preceded by the butterfly.