And there is a very broad segment that fall under the label of "non-denominational" or are otherwise independent, whose doctrine as a community is usually decided by one man.
For the sake of not derailing the discussion, I will retract all comment about "one man" since that seems to be a sticking point.
What I meant initially is not that each denomination has a "pope" ... but each denomination was generally started by one man. Luther was responsible for a group that separated from Catholicism. Calvin was responsible for a whole school of thought. And the church up the road was started by a man who disagreed with the pastor at the church I used to go to, and left, taking about 1/3 of the congregation with him to start a new church. At the start of most (maybe all?) of them is one man. Has there ever been a full and equal council that got together and decided to separate and create a new denomination, without the leadership of one man?
And what I meant above is that many non-denoms ARE started by one man, dependent upon his theology, and when a new pastor comes in, various beliefs may change, based on that man's interpretations. I've seen it happen in many churches around here. And John MacArthur is a larger example with his own church.
But it doesn't really matter to sola scriptura, so ... I will retract it as unimportant.
But when it comes down to whether those Scriptures speak of Christ ACTUALLY PRESENT in the bread and wine, or mere symbolism. Of salvation that requires perseverance, or whether it is impossible NOT to persevere. Whether baptism is a means of grace, or just a public statement. The role of women in the Church. And a thousand other questions - there is disagreement. And ALL will point to the same Scriptures (seen through their particular lens or that of their denomination) to justify their dissenting answers to those and many other questions.
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The majority of Protestants belong to churches that agree with you on every one of those doctrinal points you just mentioned. But the relatively few non-denoms or 'never was' freelance people define the issue and you say....disagreement.
On this point I disagree with you. Actual presence of Christ? Lutherans and some others will agree with Orthodoxy. But Baptists, Pentecostals of all stripes and others will disagree. Impossible to lose salvation? Those who subscribe to Calvinism and a few others will agree, but a good many Evangelicals and almost all Pentecostals will disagree. Baptism? Lutherans, Anglicans, and a few others will agree with Orthodoxy, while Baptists, Pentecostals, non-denoms, and many others will disagree. The role of women in the church is a changing issue where some Lutherans, some Baptists, and a few other small denominations resist ordination of women, while nearly all others have changed their position over the past century.
I don't think the majority of Protestants agree with me, or with each other on these issues. But I don't say that as some kind of implication that "Protestants are not united". Of COURSE they aren't. They were never really intended to be, since most of their denominations are founded on some kind of reformation, or disagreement, depending on how you look at it. The underlying desire may well be noble because I have no doubt that every one of them was motivated to seek and move closer to Truth. But the outcome has been repeated schism, as we would see it.
My point though is not to criticize Protestants, but rather I think the label "Protestant" is essentially meaningless.
However, as it relates to the discussion of sola scriptura, never mind the labels. What it DOES demonstrate is that sincere people with a love for God, doing their very best to interpret Scriptures correctly (who ever does otherwise?) can and do arrive at completely polar opposite conclusions, using "scripture alone". And that's the bottom line. We can do with that as we will, but it is a fact that I don't see how it could be disputed, as it is in very plentiful evidence.