What is significant about the fact that Gabe's trumpet will not make a sound?
In the final scene of the play, Fences, Gabriel returns to open the gates of heaven for his brother, Troy. You see, the final scene takes place on the day of Troy's funeral. Gabriel suffered a brain injury in WWII. Since his return he has called himself, "Gabriel the Archangel." He also has carried around a trumpet when it's time for heaven's gates to open on judgement day.
Gabriel decides that his brother's funeral is the day of judgement for everyone present. When he blows into the trumpet, as hard as he can, nothing comes out. Stage directions tell the reader that: "There is a weight of impossible description that falls away and leaves him bare and exposed to a frightful realization" (2.5.113). What has he realized?
We also read that: Gabriel begins "A slow, strange dance, eerie, and life-giving. A dance of atavistic signature and ritual" (2.5.113). A man claiming to be an archangel turns to atavisim and ritual?
When the trumpet doesn't make a sound, it appears that Christianity has failed Gabriel and all of those around him. The dance that appears after the realization is often interpreted as years of oppression (African slaves oppressed by white, Christian slave owners) coming to the surface. He has found his strength in his African roots - a common theme in many of August Wilson's works.
Gabriel concludes his dance with a wild howling song, and the song has an affect to allow: "the gates of heaven stand open as wide as God's closet" (1.5.113). Instead of performing his Christian judgement ritual, Gabriel has opened the way for his brother by some primal, native roots found in the connection of their African past.