This is a re-do of a question I asked yesterday but was removed because it asked about the modern day. Reading the New Testament makes Jesus seem like a based egalitarian populist proto-communist hippie. In medieval times the clergy often supported the concept of nobility and divine right, seems very opposed to Christ's original teachings. What was used to justify this? Did they even need to justify it because most were illiterate and would just take the priest's word on it (or is this in itself a historical misconception) ? Just to clarify I'm just using hippie as a term for a pacifist anti establishment populist, of course Jesus didn't make peace signs or live out of a van (as far as we know).
"Communism", "Hippie" and "Egalitarian" are all modern notions. So you are reading the New Testament with very modernist eyes. Medieval people, put simply, aren't reading those notions in the text. They are reading it, for the most part, with medieval preconceptions instead. It's no wonder then that they didn't come up with the version of Christianity that you find in the New Testament.
Better questions to ask would be "How did specific idea X in specific part of Middle Ages Y develop? How was this idea supported from the Christian Scriptures?"
Are you attempting to imply that all modern day Christians should be hippies? Medieval societies did live in what might be called communes today, including ecclesiastics (monasteries) or the laity (peasant communities; burghers in guilds, etc.). Christian ethics were also aimed at imposing what was called the 'Peace of God' in the eleventh-century.
Christian ethics were also responsible for a incredible range of violence. The Crusades, both in the Levant and Europe and the Inquisitions are the most obvious examples. The ecclesiastical elite and the lay elite usually were drawn from similar stock. Non-heir sons of the lay elite might end up going into the Church and priests who had powerful siblings or cousins would usually do quite well. The ecclesiastical class were major landholders, too, with many of the same interests of the nobility.
The medieval world believed sometimes in a way which is inconceivable to ourselves. Movements emerged like the mendicant orders who attempted to distance themselves from real wealth (and ironically in doing so became exceedingly wealthy). The world was varied and confusing, even to contemporaries, and it is not easy to justify why one writer or priest might disdain or uphold the world in which he lived.
Finally, however you might read the New Testament is quite different to how a medieval priest/monk might. They would have spent years learning and debating articles of faith and were probably better situated to use it to understand their world than you are to yours.