During the fourth century, Christians debated the meaning of key Bible verses in order to establish two competing visions of who and what Christ is.
One group that we call the Arians argued that while the Son is divine, the Bible naturally distinguishes him from the Father.
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By contrast, the pro-Nicenes (or those who would become Nicene) argued that the Father and share one divine nature.
Of the many passages debated, John 14:28 played a key role for the Arian position: “I am going to the Father, for the Father is greater than I.”
Since 1 Timothy 6:16 defines the nature nature as unseeable, and Christ is evidently seeable, the Arians argued the Father is greater than the Son because he is invisible.
And God, as Paul says, “alone has immortality, who dwells in unapproachable light, whom no one has ever seen or can see.” This God alone, they argued, was God the Father. God the Son, though divine, was seeable and visible and therefore had a distinct nature from God the Father.
This argument develops across three stages in the 300s. The conclusions remain basically the same from Arius to the Latin Anti-Nicenes and the Greek Eunomians, but the exegetical arguments and conclusions become more precise and sophisticated.
First, Arius in the early 300s argued that the Son was the product of the Father’s will, and thus divine yet not precisely consubstantial with the Father. After all, God alone was ungenerate while the son was generated or begotten of the Father.
There can only be one invisible and immortal God according to 1 Timothy 6:16. That is God the Father.
Second, mid-300s Arians began to argue that the Son was the visible of the invisible Father. Since 1 Timothy 6:16 identifies God as invisible and since the Son is the visible of the invisible, the Son is divine but in some distinguishable way at the level of nature.
They were able to use the traditional notions, present in Tertullian, that the Son preexists because he was manifest in the OT theophanies. They granted the point, but then pressed that he is by nature able to be seen. The Father by contrast cannot be seen.
He is ingenerate by nature; the Son is generate by nature.
Late 300 Anti-Nicenes agreed with the visibile-invisible binary, seeing the Son as uniquely visible because he is the Person revealed in OT theophanies not the Father. But they also pressed the question of who or what God the Father sent in the Incarnation?
Does the Son only submit in his human nature? Did the Father only command the humanity of Christ? They affirmed that God sent the whole Son---and that means the Son by nature submits to the Father.
These (and earlier) anti-Nicenes or Homoians regularly used John 14:28 to make their arguments (Barnes 186). During the Council of Aquileia, Ambrose asks Palladius where the Bible says the Son is inferior to the Father? Palladius pointed to John 14:28.
Ambrose, likely frustrated, says that John only refers to the body of Jesus (i.e. what was created).
Palladius simply and effectively replied, “Well, then, was only the body sent and not the Son as well?” The point is: Did the Father only send the human nature of Christ?
Michel Barnes identifies Palladius’s question in summary form as: “What or who is sent in the Incarnation?” (Augustine, 187). Augustine in De Trinitate I will answer this question but cannot simply say the less passages speak of humanity and the greater passages of divinity.
If John 14:28 refers to the Father sending the humanity of Christ, what does that even mean? Granted, the word “send” is not used, but Palladius presumably thinks it’s implied by the context of John 14.