Who's the only true God?

In response to my review of the Tuggy/Brown debate, I've been asked some questions about my interpretation of Jn 17:3, so I'm going to expand on my explanation. On the face of it, Jn 17:3 is the strongest unitarian prooftext. It's downhill from there. 

There are two possible ways to construe "the only true God". 

A. View it as an idiom for Yahweh. In the OT, Yahweh is the only true God. So this is an alternative designation for Yahweh. 

1. Compare these two statements:

How can you believe, when you receive glory from one another and do not seek the glory that comes from the only God [monou theou]? (Jn 5:44)

And this is eternal life, that they know you, the only true God [monon alethinon theon], and Jesus Christ whom you have sent (Jn 17:3).

These are verbal variations on the same idea. Two slightly different ways of saying the same thing. It's not as if the less specific descriptor in 5:44 might be open to more than one God, while it's the addition of "true" in 17:3 which narrows it down to just one God. So "the one God" and the "one true God" are equivalent designations. And they have their counterparts in OT usage (e.g. 2 Kgs 19:15,19; Ps 85:10; Isa 37:20). So on this view the three-word designation in Jn 17:3 is an idiomatic synonym for Yahweh. To paraphrase:

And this is eternal life, that they know you, Yahweh, and Jesus Christ whom you have sent (Jn 17:3). 

But since it's written in Greek rather than Hebrew, it doesn't say "Yahweh", even though that's the conceptual meaning. 

2. Which doesn't mean the Father is the only Yahweh, as if you break up three-word designation into a two-word unit ("the true God") modified by "only". It's not like "the true God" might refer more than one God, so you need that extra qualifier ("only") to confine the "true God" to just one true God. No, the entire three-word designation functions as a semantic unit. An idiomatic expression for Yahweh. 

Whether or not the Father alone is Yahweh depends on what else the Fourth Gospel says about Jesus. The Fourth Gospel has other passages which identify Jesus as Yahweh, too (e.g. Jn 8:58; 12:41; 18:6).

B. Another way is to view each word in the three-word phrase as having a separate meaning, so that the overall meaning of the phrase is a combination of each semantic verbal unit: "one" plus "true" plus "God"

And on that view, the same Gospel says Jesus is the one true God–if you simply combine Jn 1:18 with Jn 14:6. Pretty simple. 

C. That depends on how we answer two questions regarding Jn 1:18. For starters, is monogenes theos the original reading? There are several supporting arguments:

1. Text-critical:

i) It's the best attested reading.  The reading in our earliest and best manuscripts. So it meets an external textual criterion. 

ii) It's the harder reading (lector difficilior potior). It is much easier to see how scribes would assimilate the jarring monogenes theos to monogenes huios (Jn 3:16,18) than the reverse. So it meets an internal textual criterion. 

2. Literary:

Calling the son "God" in 1:18 forms an inclusio to 1:1, while both form an inclusio to Jn 20:28. 

3. Theological:

i) Jesus doesn't reveal God in the way human prophets like Moses and John the Baptist do. Indeed, in John's Gospel, both are said to witness to Jesus. So Jesus is not just another prophetic witness to God. 

ii) What makes Jesus the ultimate revelation of the Father is a like-reveals-like principle: only God can fully reveal God. Like father/like son. 

Not a "son of God" in the metaphorical human sense, because that underscores the disparity between God and man, whereas, if both share the same ontology, then one mirrors the other.

4. Precedent:

The comparison and contrast between the invisible God (the Father) and the visible God (the Son) dovetails with the 2nd Temple doctrine of the two-Yahwehs. 

D. A second question: does monogenes mean "only-begotten" or "one and only"? Most modern commentators and lexicographers think it means "unique, one of a kind". 

E. Combining both answers, Jn 1:18 calls the Son the "one and only" God. If anything, a monogenes theos (Jn 1:18) sounds even more exclusive than a merely monos theos (Jn 17:3). Not just "one God", but a "one of a kind" God. In a class by himself. 

F. While we're on the general subject, what about 1 Jn 5:20? Is Jesus "the true God"? There are several supporting arguments:

1. Grammatical:

i) As the nearest antecedent to the demonstrative pronoun, "Jesus Christ" is the default referent. While that's not conclusive, the syntax creates a presumption which must overcome. 

2. Theological:

i) The very fact that the object is somewhat ambiguous in 1 Jn 5:20 (is it the Father or the Son?) is, in itself, an argument for the deity of Christ. In the very next verse, and concluding statement, John warns his readers to keep themselves from idols. Now what could be more idolatrous than to regard Jesus as God if in fact he isn't God? Nothing is more fundamental to John's Jewish piety than the identity of the true God. If John thinks the Father alone is divine while Jesus is not divine, how would he possibly leave his readers scratching their heads about which one is the true God in v20? 

ii) Furthermore: 

R. Schnackenburg,82 who has given us the best commentary on 1 John, argues strongly from the logic of the context and the flow of the argument that "This is the true God" refers to Jesus Christ. The first sentence in 5:20 ends on the note that we Christians dwell in God the Father ("Him who is true") inasmuch as we dwell in His Son Jesus Christ. Why? Because Jesus is the true God and eternal life. Schnackenburg argues that the second sentence of 5:20 has meaning only if it refers to Jesus; it would be tautological if it referred to God the Father. His reasoning is persuasive, and thus there is a certain probability that 1 Jn 5:20 calls Jesus God—a usage not unusual in Johannine literature. R. Brown, "Does the New Testament Call Jesus God?", Theological Studies 26 (1965), 558.

iii) In addition, Jesus is the source of eternal life because he is the life-giving God. His protological role as the Creator God of Gen 1 (Jn 1:1-5) is the basis for his eschatological role as the Resurrection and the Life (Jn 11:25). 

3. Literary: 

Just as there's an inclusio pattern in John's Gospel (see above), we have the same pattern in 1 John. Is it coincidental that we have a climatic statement about Jesus at the end of 1 John (5:20)? Like John's Gospel, 1 John opens with a programmatic statement about Jesus, then circles back:  

1That which was from the beginning, which we have heard, which we have seen with our eyes, which we looked upon and have touched with our hands, concerning the word of life— 2  the life was made manifest, and we have seen it, and testify to it and proclaim to you the eternal life, which was with the Father and was made manifest to us (1 Jn 1:1-2).

And we know that the Son of God has come and has given us understanding, so that we may know him who is true; and we are in him who is true, in his Son Jesus Christ. He is the true God and eternal life (1 Jn 5:20).

G. While it's rare, calling Jesus "God" in the Johannine corpus is not a random occurrence, but happens at strategic junctures. The prologue to John functions like the prologue to Job. The narrator lets the reader into secret that characters in the narrative don't know (at least not initially). The reader then watches the characters discover what the reader already knows. The exclamation of Thomas forms an inclusio to the Prologue. In his epiphany, Thomas realizes something the reader knew all along. What the reader knows by description, Thomas knows by experience. And 1 Jn 5:20 fits that strategy.