We declare, however, that the Son also, considered in Himself (as the Son), is invisible, in that He is God, and the Word and Spirit of God;
…When as we read in the Gospel, “Moses appeard talking with Jesus”—it is evident that in early times it was always in a glass, (as it were,) and an enigma, in vision and dream, that God, I mean the Son of God, appeared—to the prophets and the patriarchs, as also to Moses indeed himself. And even if the Lord did possibly speak with him face to face, yet it was not as man that he could behold His face, unless indeed it was in a glass, (as it were,) and by enigma.
Tertullian
Against Praxeas
Chapter XIV