Biblical, Fragmented
Just quoting the Bible all the time is for amateur hour: Baldwin writes his entire novel in a biblical style. Using phrases from the Bible to fill its long, wordy sentences, the novel has an authoritative style. We respect this authority, totally:
[…] John's heart was hardened against the Lord. His father was God's minister, the ambassador of the King of Heaven, and John could not bow before the throne of grace without first kneeling to his father. (1.1.37)
"Heart was hardened," "ambassador of the King of Heaven," "bow before the throne of grace"… all these phrases are echoes of the Bible. Hey, you know what they say: good artists copy, great artists steal.
As far as structure goes, hoo boy. This novel jumps all over the place, every which way. There's an overarching, linear structure, but the narration keeps zipping back in time, filling us in with information on the characters by telling us their history. If you get motion sickness, take a Dramamine before cracking this bad boy.
For example, look at the way the narrative stops short and jumps back in time through Florence's memory:
The piano had stopped. All around her now were only the voices of the saints.
"Dear Father"—it was her mother praying—"we come before You on our knees this evening to ask You to watch over us and hold back the hand of the destroying angel." (2.1.10-11)
In the first paragraph, Florence hears the voices of the saints, meaning the other people in the church with her in Harlem. But after the break, a different kind of praying picks up, in the voice of her mother. This zigzagging through time gives the novel a fragmented feeling, sometimes disorienting the reader.