Where I must profess ignorance is the Council of Nicaea. My reading on the subject was decades ago, and what I remember was that Matthew, Mark and Luke were called the synoptic gospels. Mark was the oldest, written approximately 70 years after the death of Jesus. There are portions of each that are virtually identical to the other 2, leading scholars to speculate that an older document called, (and I'm not kidding) Document Q was the basis for parts of the 3 synoptic gospels. So the first hand accounts of many of the actions in the life of Jesus are known to us from an unknown document.
Jesus died an outlaw. His followers kept his memory alive in secret. The secret greeting among Christians was for a person to draw a line on the ground:
If you were a fellow Christian, you completed the image:
We remember the symbol of the fish, but we really don't think about the nature of Christianity as an outlaw religion was until the Emperor Constantine converted. There was no keeper of the records after Jesus died or ascended into heaven. There were other records of the life of Jesus which did not make it into the canon.
My favorite scene in
The Life of Brian is when
Jesus is preaching the Sermon on the Mount. The camera pulls slowly back through the multitude assembled, and as it does, Jesus's voice becomes fainter and fainter. This leads to people in the back of the crowd wondering why Jesus said "Blessed are the cheese makers" and why "The Greeks shall inherit the earth".
When people talk about Christianity, I feel like I'm like one of the people at the back of the crowd at the Sermon on the Mount. I'm not sure we're hearing everything Jesus said correctly. I'm not trying to say anything nasty about the life of Jesus. But when we say something is 'the Gospel truth', I wonder what that really means.