How preposterous. It was well known and understood from Jesus teaching. Even the apostles called Him God. He said He was the “I am”, and it was His Holy Spirit that was sent as councilor which was clearly understood by the apostles and all they taught.
Easy to say preposterous when you have the benefit of thousands of years of Scriptural scholarship and theology to point you in that direction.
Where in Scripture is the actual theology of the Trinity laid out for us to understand? It isn’t because it was not understood then in the way we understand it now.
The Jewish people fiercely rejected the notion that Jesus was God and were sure that these followers of His were polytheists as there is no clear presentation of the doctrine of the Trinity or God as one in three persons.
We have the benefit of all that the Church was led to declare as Scripture laid out for our study at our leisure. The early Church did not have that.
And speaking of it being well known and understood, that is a wrong assertion which is clearly seen in all the heresies that arose regarding Jesus. These heresies are alive and well today.
If all that Jesus taught was well known and understood, then the NT could have stopped at the four Gospels.