Lilla D. answered 03/30/20
Multilingual Tutor Specializing in Japanese/Languages/Reading/Writing
You basically got it - it would be, a voice from (out of) the light falls off the face of the sky. Think of, mir fällt ein Stein vom Herzen - literally, a stone falling off of your heart, right? It's the same construction - so the dative (dem) Himmel is the thing which is losing an object, so to speak, and the von + dative (vom) Gesicht is the place where the object is falling off of, and the nominative (eine) Stimme is the subject, so it's the object doing the falling.
Hope this helps :)