One key challenge that Augustine counters in Book II of his On Trinity is the question regarding the invisibility of Jesus in His essential nature. The antagonists argued that Jesus as the Son of God was always visible to the Father; therefore, this visibility also implies mortality and changeability. Two texts that Augustine quotes are:
- Now to the King eternal, immortal, invisible, to God who alone is wise, be honor and glory forever and ever. Amen. (1Ti 1:17 NKJ)
- He who is the blessed and only Potentate, the King of kings and Lord of lords, who alone has immortality, dwelling in unapproachable light, whom no man has seen or can see, to whom be honor and everlasting power. Amen. (1Ti 6:15-16 NKJ)
Augustine maintains that the invisibility of God means that the Triune God (Father-Son-Spirit) is invisible.
The antagonists argued that the Son was visible not only in flesh through His incarnation but even before that in Himself, and so visibly appeared to the fathers. And, since He was visible in His pre-incarnational existence, He was also mortal, they said. And, so they argued that 1 Timothy 1:17 speaks only of the invisibility of the Father. Further, in that same sense, the Holy Spirit is thought to also be mortal, because He also was visible once as dove and at another time as fire. Both the Son and the Spirit were visible to mortal eyes in various forms and various times, all implying, according to the antagonists, that both the Son and the Spirit were visible, mortal, and changeable; therefore, 1 Timothy 1:17 cannot apply to them but only to the Father.
Augustine begins by asking who the contenders think was walking in the Garden of Eden from whose face Adam hid. Was it the Father or the Son? Why not the Father, especially when the form of the narrative signifies no change of the Divine Person from chapter 1 to chapter 3. If we understand that the world was made by the Father through the Word, why not also accept that Adam saw the Father in a visible form. In fact, the visibility of the Father is not impossible in the same way as the audibility of Father was not impossible (as in John 12:28 and Matthew 17:5 when His voice is heard apart of the Spirit and the Son). Obviously, the voice was not of the Spirit; for, nowhere is Jesus called as the Son of the Holy Spirit. ‘But here, where it is written, “And the Lord God said to Adam,”‘ says Augustine ‘no reason can be given why the Trinity itself should not be understood.’
Augustine goes on to examine the theophanies to Abraham, Lot, Moses, the Israelites in wilderness, and to Daniel. Why not accept the three-person appearance to Abraham as the visitation of the Trinity, especially when none of them is shown to be lesser or greater to the other? Next, the two angels that appeared to Lot could be understood to be the Son and the Spirit, since They say that They were sent, and nowhere does it say that the Father is sent; however, He is the sender. The goal of Augustine is to show that visibility cannot be limited to only the Son and the Spirit, but even the Father can be seen as being visible at times. However, in His divine nature, the Triune God cannot be seen corporeally, “but we must believe that by means of the creature made subject to Him, not only the Son, or the Holy Spirit, but also the Father, may have given intimations of Himself to mortal senses by a corporeal form or likeness.”
See Augustine On Trinity, Book II.