Those are cosmetic changes. But Harpur's rejection of the Church's model of Trinitarian Theism in favor of a Unitarian model has not been accepted. More books have been written to explain, and show the implications of the Trinity in the past twenty years than ever before. Harpur claims that he remains a Christian by his faith in the resurrection (p.80) but the dialogue with Islam has made clear that Islam also believes in the resurrection and the resurrection of Jesus in particular. The one point at issue is whether Jesus is the Son of God, and Harpur joins with Islam and the Jehovah's Witnesses in denying this.
Harpur is right that the doctrinal explanation of the Trinity only occurred much later in the history of the church. He does not mention this, but the term Trinity was first used by Tertullian in his books against Marcion and Praxeas (c.207 and c.213). In that sense he was right to say that "You simply cannot find the doctrine of the Trinity set out anywhere in the Bible" (p.8). The fuller explanation of the model came much later with the Cappadocian Fathers.
But he totally failed to tangle with the fact that there are two models of the oneness of God. Is God a mathematical oneness that decided to make humans to judge them? Or is God an organic complexity of Persons within the oneness of God. He thinks Mark's Gospel was written about 64 AD. And Mark, which we view as the report of an interview with Peter (see Introduction to our Mark Commentary). refers to the words from heaven at Jesus' baptism "You are my Son, the Beloved; with you I am well pleased" (Mark 1:11, repeated in Matthew 3:17). The Great Commission is also obviously Trinitarian. "Go therefore and make disciples, baptizing them in the name of the Father and of the Son and of the Holy Spirit" (Matthew 28:19). This commission is unthinkable in a Unitarian model of God. And it is also clear that the Apostles Creed soon set out the syllabus of what Christians should be taught about the Father, the Son, and Spirit. This was clarified further in the Nicene Creed, which has remained the agreed model of instruction for Christians of all denominations everywhere.
Harpur points out that Paul does not call Jesus God (p.8). But this misses the fact that Paul says "he was declared to be the Son of God with power according to the Spirit of holiness by the resurrection from the dead" (Romans 1:4). He also speaks of "peace from God our Father and the Lord Jesus the Messiah (Romans 1:7; 1 Corinthians 1:3; 2 Corinthians 1:3, see 13:13; Galatians 1:3; Philippians 1:2, see 2:6, Colossians 1:3, 1 Thessalonians 1:1, 2 Thessalonians 1:2). Faith is in Jesus the Messiah (Romans 3:22), not in God the Father, and the Son is to reign till he hands over the Kingdom to the Father (1 Corinthians 15:24-28).
The many references in John's Gospel to Jesus divinity and relationship to the Father are too easily dismissed by Harpur's pronouncement that "the fourth Gospel cannot be taken literally when Jesus makes extraordinary claims about himself" (p.57-58). But whatever scholars believe about the authorship and teaching of John's Gospel, it is obvious that the very Trinitarian model that John presents (without using the term Trinity) was in existence among some Christians in the first century.
When he wrote in 1985 Tom Harpur did not even mention the Holy Spirit. Since then there has been a huge literature about the work of the Holy Spirit in the Old and New Testaments, and how the Spirit works as the third Person of the Trinity. It now seems very hard to think of God as a loving God apart from a model in which there is a loving complexity within the oneness of God.
The difference between a Unitarian model of God and a Trinitarian model is not settled by discussing this and that item of history. The first thing is to clarify how the two models differ then to decide how one intends to live one's life. I have decided to live and preach the Trinitarian oneness of God in the Church from the New Testament. That is a given. I intend to keep talking to the Father as a little child with his parents. I talk to the Son of God, who forgives and welcomes me into his family, and then invites me to share in his world-wide reign. I look to the Holy Spirit for inspiration and power to produce in me the fruit and gifts which I need to live in the rich fellowship of other Christians. There is no logical proof that I am right. If I should be wrong (as in Pascal's wager), I have nothing to lose by living this way. And if I am right I have everything to gain.
What could Harpur's model offer? Joining the Unitarian denomination
does not appeal to me at all; becoming a Muslim sounds even less appealing;
and becoming a Jehovah's Witness to go from door to door denying the Trinity
is even more dismal.