Tertullian

“ And by parity of reasoning, if He is the same who was visible after (coming in) the flesh, how happens it that He is now declared to be invisible by the apostles? How, I repeat, can all this be, unless it be that He is one, who anciently was visible only in mystery and enigma, and became more clearly visible by His incarnation, even the Word who was also made flesh; whilst He is another whom no man has seen at any time, being none else than the Father, even Him to whom the Word belongs? Let us, in short, examine who it is whom the apostles saw. ”

“ It was of Him, too, that he had said in a previous passage: “Now unto the King eternal, immortal, invisible, to the only God;” [15] so that we might apply even the contrary qualities to the Son Himself—mortality, accessibility—of whom the apostle testifies that “He died according to the Scriptures,” [16] and that “He was seen by himself last of all,” [17] —by means, of course, of the light which was accessible, although it was not without imperilling his sight that he experienced that light. ”