"a patchwork of distinct documents and traditions that were later compiled and edited"
If this sort of thing sounds interesting, I highly recommend reading about the formation of the New Testament and especially the non-canonical gospels. Here's a splurge of my recent learning.
Until around 200AD, the early Christians followed a wide variety of gospel texts. The (anonymously authored) synoptic gospels which we now label Matthew, Mark and Luke were written a couple of decades after Jesus' death. They overlap a lot and mostly describe his life and teachings without much theological wrangling.
What we now label as John was written around 100AD. It deviates from the synoptics, taking a strong stance on the divinity of Jesus, and talking about God being his father.
Then there were a lot of so-called Gnostic texts. The gospels of Thomas, Mary, Judas, Peter, James, Egyptians, Hebrews, Truth and so on. These were probably written between 100 and 200AD. Until an archeological discovery of many Gnostic texts in 1945 (the "Nag Hammadi" library), many were only known via references or fragments. They tell a different story to modern Christianity, describing the material world as a sort of awful cosmic accident which we can escape by means of learning secret knowledge. Jesus is often depicted as a mortal who has been given that knowledge, and has privately passed it on to his disciples. Some Gnostic communities were thought to have experimented with breaking gender and sexual norms. After all, what is the point of conforming to biological expectations when biology is part of a material illusion? This is in stark contrast to mainstream Christianity which teaches that man and woman were made that way as part of God's perfect design.
In 180AD an early church father named Irenaeus published a text "Against Heresies", canonicalising John alongside the synoptics. This ignited the suppression of Gnostic Christian communities and the destruction of their texts. We can't know exactly why he did this, but can speculate: to unify the religion around a central doctrine, to affirm the importance of church authorities, and to give Christianity a safe ideological basis that appealed to the intellectual strata.
Nevertheless, strands of Gnostic thought were preserved. For example, the Middle-Eastern "Mandaeans" have a religion with strongly Gnostic themes. They revere John the Baptist as their most important prophet, see the material world as created by an evil demi-urge, and view human souls as sparks of light trapped in the world and trying to break free.
Various Quran passages also reflect Gnostic thought, such as the mortality of Jesus, and stories of the infant Jesus and Mary that are absent from the canonical texts but seen in Gnostic texts. It seems likely that Muhammed engaged with surviving Gnostic communities (such as the Mandaeans) and learnt about their beliefs before reframing them in the Quran.
