They looked elsewhere for the rule of faith and thought they found it solely in the Bible. Its interpretation would be left to the individual reader, as guided by the Holy Spirit. But reason and experience tell us that the Bible could not have been intended as each man's private guide to the truth. If individual guidance by the Holy Spirit were a reality, everyone would understand the same thing from the Bible since God cannot teach error. But Christians have understood contradictory things from Scripture.
Fundamentalists even differ among themselves in what they think the Bible says.
The Bible also tells us that private interpretation is not to be the rule for understanding the Bible. Later he warns what can happen if a person ignorantly approaches Scripture on his own or is unstable in clinging to the apostolic teachings he has received. Private interpretation and instability in clinging to the doctrines passed down from the apostles can thus result in one twisting the Scriptures to one's own destruction. The Bible also denies that it is sufficient as the Church's rule of faith. The Reformers saw justification as a mere legal act by which God declares the sinner to be meriting heaven even though he remains in fact unjust and sinful.