New Testament scholar Maurice Casey once claimed that “The Gospel attributed to St. John is the only New Testament document in which the deity and incarnation of Jesus are unequivocally proclaimed.”
This statement is somewhat misleading. If the proclamation of the Gospel were really unequivocal, it would be hard to explain the extended christological controversies in the early church (see Henry Chadwick, The Early Church).
For example, the third clause of John 1:1 may be translated either “the word was God” or “the word was a god.” Justin Martyr apparently understood the passage in the latter way. According to Henry Chadwick, “Justin had boldly spoken of the divine logos as ‘another God’ beside the Father, qualified by the gloss ‘other, I mean, in number, not in will.'” (Justin, Dialogue with Trypho 56; 127; 129; Chadwick, Early Church, 85-86.)
In a footnote Collins writes,
B.A Mastin considers it “overwhelmingly probable” that John 1:1 “describes the pre-existent Logos as God”. This conclusion, however, is based on his view that Thomas’s acclamation in 20:28 “is the one verse in the New Testament which does unquestionably describe Christ as God”. This view fails to recognize, however, that the phrase dominus et deus, and presumably its Greek equivalent, is an honorific acclamation, used, eg, by those who wished to flatter Domitian.
Domitian was Roman emperor from 81 to 96 – about the same time the Gospel was written. The implication is that the author of the Gospel of John has Thomas proclaim Jesus to be the true dominus et deus, a rather politically subversive and dangerous move. It is more likely that John understood Jesus to be divine in some sense, yet not identical with God the father, the Most High God. This makes it possible to understand the plain meaning of verses such as this:
Now this is eternal life: that they know you, the only true God, and Jesus Christ, whom you have sent. John 17:3
Trinitarians (in my experience) have to labour long and hard to explain this verse in a manner consistent with their theology because the verse clearly distinguishes between God on the one hand and Jesus, on the other. They are depicted as separate beings. Jesus is the lesser person (“the Father is greater than I” – John 14:28). But Jesus is given divine status by his Father, the only true God.
The first three paragraphs are taken from King and Messiah as Son of God Divine, Human, and Angelic Messianic Figures in Biblical and Related Literature by Adela Yarbro Collins and John J Collins, pp 175-176. The Collins’s are both professors of the Bible at Yale University. The concluding paragraphs are mine.