Certainly some things need interpretation and tradition is used by all sides. However, for the fundamental basics of things such as the identity of Christ, belief, the idea of sin, the existence of heaven and hell, and the elements of needing salvation etc., I don't think much needs to be explained. I still think a child could only read the Bible and know enough to be a Christian.
I've never thought of Luther and Calvin as "failed priests" before, but I can see how you would see it that way. My guess is that they had much more credibility as heroic whistle-blowers than they otherwise would have, so I thank God they were priests.
There is a vast difference between the OT prophets who condemned the actions of the people (the Church) but DID NOT START THEIR OWN GROUP OF WORSHIPPERS, and Luther and Calvin, who invented their own way of worshipping God. God NEVER erased His People and began a new one. The prophets were "whistle-blowers", but they always remained within the Church.
Your comparision fails.
Regards
We just got through discussing the necessity of baptism in John 3, pretty fundamental concept. The identity of Christ is a matter of interpretation; the early Church spent several centuries combatting christological heresies, and we still have the Latter Day Saints belief system, and all read the same scripture. A child could read the scripture and know enough on his level of understanding, but if his parents are heretical, the child would most likely grow up a heretic.
heroic whistle-blowers [...] I thank God they were priests.
I am actually not sure if Calvin was ever a priest. In the case of Luther, I think that before his apostacy his contribution was positive as he posed important questions that needed answering, but that would not have set him apart from numerous Catholic reformers who remained faithful and produced the necessary reform at Trent. His rebellion, desecration of his vows and the mutilation of the Christian Canon did nothing good to anyone.