Original: Each of Bach's cello suites contains a sarabande, and the film uses the sarabande from his fifth suite, which Bergman also used in Cries and Whispers (1971). The sarabande from the second Bach suite serves as the primary theme in Bergman's Through a Glass Darkly (1961).
Simplified: It uses the sarabande from the 5th suite for solo cello by Bach.