The Chorus in Marlowe's Dr. Faustus, the inspiration for Goethe's Faust Parts I & II, serves two purposes. First, it is transitional and, second, it is expository. The first purpose of the Chorus is to provide transitions into and/or out of elements of the play, reminiscent of Greek Choruses.
The second purpose is to provide enlightenment into Dr. Faustus's behavior and character in addition to giving the audience information that Faustus himself doesn't have, thus serving in a prescient and foretelling capacity. The objective of the Chorus's function is to increase suspense as the audience moves through the saga with Dr. Faustus.