That is not entirely true. God would not leave us without a way to absolutely understand and follow His will for us is. And indeed He did: 2 Tim. 2:15. That is God’s pattern for us to follow if we want to be approved workmen who need not be ashamed when we stand before Him.
There are some very “main and plain”, repeated doctrines in the Bible such that we don’t need some earthly authority to tell us what it means (usually to the empowerment of said authority).
God gave us the indwelling of the Holy Spirit to makes sense of His Word as well.
Besides, there are easily proveable historic “misinterpretations” by that earthly “authority” that discounts any claim to authority at all.