Plain truth? If you get 100 Protestants to describe God's Plain Word of Truth, you'll wind up with 125 descriptions.
Once one takes it upon one's self to proclaim doctrine, why then, anything goes. Jesus created the teaching Church. All of the Gospels and Epistles hammer home the role of the Church as teachers and the need for orthodoxy. The role of the Reformation was to convince people that there was no need for orthodoxy and that anything that they happened to imagine that morning was as good as anything else anybody else could come up with. Including the Tradition of the Church and the Teachings of the Apostles, Apostolic Fathers, and Church Fathers.
AS I said, protestantism is a SEA of confusion.
That is why the Church is called the Barque of Peter, as it was/is from there that Jesus calms that raging sea.
As we have seen during its 500 year history, protestantism is a raging storm of doctrine and personal theology with no rudder and that is why so much heresy like huge waves tosses it about.