The Gregorian chant is Procedamus in pace!,
performed by Choralschola der Capella Antiqua München (conducted by Konrad Ruhland). This chant was recorded in Pfarrhof Reuth, Aicha vorm Wald, Germany, in January 1976. It appeared on a CD called Paschale Mysterium, released in 1977. The CD featured other chants performed by Choralschola der Capella Antiqua München, all conducted by Ruhland.
The fundamental beat is very similar to the beat in Soul II Soul's Keep on Movin' from 1989. This also applies to Sadeness (Reprise), Hallelujah, The Rivers of Belief, Sadeness part I (Extended Trance Mix), Mea Culpa part II (Fading Shades Mix), and remixes of The Rivers of Belief.