Complex sentence: The outer sections, in E major, are of an otherworldly tranquility, while the central section is intensely turbulent: it breaks suddenly into the tranquility in the unrelated key of F minor.
Split into simpler sentences: The outer sections, in E; major, are of an otherworldly tranquility. The central section is intensely turbulent; it breaks into the tranquility all at a sudden in the unrelated key of F minor.