Complex sentence: The chorus is structured in symmetry in seven sections, an instrumental sinfonia of all instruments, the themes in the choir, a choral fugue, a reprise of the sinfonia with the voices added, then a variation of sections 2 to 4 as 5 to 7.
Split into simpler sentences: The chorus is structured in symmetry in seven sections, an instrumental sinfonia of all instruments. The fourth section is a reprise of the sinfonia with the voices added, then a variation of sections 2 to 4 follows as 5 to 7.