There are more cross inscriptions in the fifth movement of Saint-Saëns' Christmas Oratorio, but I don't know if there's any significance to these.
The text here is a copulative sentence ("Deus meus es tu" - literally "God mine are you," but in a smooth translation, it's "You are my God"), and as one voice sings the subject and verb ("tu es"), the other sings the predicate nominative ("Deus"), so the overlap of these two voices illustrates the meaning of the sentence.
