The article was written by well respected scholar James Dunn, and this is from an article in Explorations vol 8, Num 2, 1994. (bolds are mine for emphasis)
1. Monotheism.
The simple answer is that Christianity lost the clarity of a belief in God as one, that is, one without further qualification.
Of course, Christianity continued to claim that it is and always has been a monotheistic faith. But there is no doubt that the doctrine of the Trinity, … Read the rest