How do proponents of Sola Scriptura choose the "correct" interpretation of a key Bible verse?

I think it would help to try to explain more what 'sola scriptura' means. The Wikipedia article on sola scriptura, for ex., says "While the scriptures' meaning is mediated through many kinds of subordinate authority [...] sola scriptura in contrast rejects any infallible authority other than the Bible." Sola scriptura is really about telling the Magisterium to go jump in a lake when they claim infallibility.

I think Sola Scriptura can more usefully, therefore, be defined negatively. Sola Scriptura means to not ascribe infallible authority to any men. Outside of that, if something doesn't seem 'clear', it's not that important, and you do the best you can using all sorts of tools to figure out what, exactly, is clear.

To be continued ...

Some key doctrines like the Trinity and the dual nature of Christ seem to require me to trust in the judgment of early councils of Nicaea and Chalcedon to favor one particular interpretation of Bible verses related to God and Jesus.

1- the assistance of Holy Spirit in my heart,

2- the binding authority of those early ecumenical councils

3- several peers that I trust, that they're engaged in the same project as myself, to collaboratively understand God and his scriptures under the Spirit's guidance

We'll look at each of these points, but consider that there is no mandate for majority rules. There is no reason to think/believe that any one of the wildly varying organised groups has it right. There is no Biblical precedent for safety in numbers.

• Noah - saved alone with his family and the 'whole earth' perished.
• Jesus - the Pharisees were wrong, the whole system was outdated.
• Abraham - alone, chosen to start a new paradigm which will eventually replace all other systems and beliefs.
• The prophets were also 'alone' working to call back all the wayward people to God.
• The Apostles were dedicated to opposing wrong-headed notions among God's people.
• The indication from Revelations is that only 'a few' will be among the firstfruits.

Thus, the 'key doctrines' may well be consigned to the majority that are not privy to the truth God has provided. While He has provided the absolute truth and it is plainly visible and coherent, many have been misled to untruth having been deceived to accept the 'doctrines of men'.

And in vain they worship Me, teaching as doctrines the precepts of men. Matt 15:9

The 'Trinity and the dual nature of Christ', are such doctrines of men - being plainly not only unBiblical, but also widely refuted by a simple reading of what God had provided.

Instead of relying on such apparent authorities, we could abandon these contrived ideas and search Scripture anew for the way to understand the difficult passages, believing quite firmly that Scripture can, does and should interpret Scripture. This approach taken by only a few, can then render such human doctrines totally redundant and shown to be errant constructs.

1 - the assistance of Holy Spirit in my heart. This is fine but it needs to be coupled with the Biblical record. Many wayward ideas have flourished under the mantra, 'the Spirit told me'. Additionally, the spirit would not countermand what Scripture expresses.

2 - trust in the judgment/binding authority of early councils

When these present a Jesus we are warned about, the obvious conclusion is that they have no credibility and should be summarily dismissed and distrusted completely! To trust in them is to invite deeper error and to move further away from the true source provided which speaks of a human Jesus who is not, and cannot be God, 'made like us in every respect' (Heb 2:17) and who is the 'firstborn of all creation' (Col 1). A multitude of counsellors are important, if only to compare with a simple reading of many passages. If they begin to deviate and get into complex and unBiblical ideas, then you are able to rule out such interpretations and favour those with greater authenticity.

3 - several peers that I trust. Also, a fine standard as fellowship is critical, but again the basis must be trust in the Biblical not the human.

How do proponents of Sola Scriptura choose the "correct" interpretation of a key Bible verse?

We allow God to interpret Himself - which he has done perfectly adequately and dismiss human self-appointed dispensers of ideas and theories not remotely support by the Bible unless one uses contrived readings of a few verses in isolation to support such constructs.

As noted earlier - there is no safety or surety in what the masses believe, none. There is every indication that the masses (organised religion) are wrong and not to be followed or trusted. God did not send Jesus to start a religion. He sent Jesus start a new chapter that would lead to the end of this age and that based on truth which only a few would be able to accept.

Enter by the narrow gate. For the gate is wide and the way is easy that leads to destruction, and those who enter by it are many. 14For the gate is narrow and the way is hard that leads to life, and those who find it are few. Matt 7:13

Finally,

As a Christian we can speculate all day long...

Indeed, and many rely on the speculations of the church fathers who devised another way to understand God and His son which is not based on any firm Biblical evidence when the text is considered wholistically.

While it is extremely difficult to do, we must be willing to potentially abandon our most cherished beliefs and start over. Not starting with a presupposed anything inherited from anyone - no matter how esteemed. Reading the Bible through a lens or filter of human origin will not lead to the simple truth God has provided. Many of the key doctrines cherished by Christendom are not legitimately found in Scripture except by special readings done in isolation. And when salvation is officially framed around these alleged truths and the masses follow, one must hesitate and question the power and influence behind such mandated adherence God never said anything about.

Study the original text

Learning Hebrew and ancient Greek would be ideal. (It is often expected that serious scholars, including priests/pastors, will do so.) Failing that, familiarize yourself with "literal" translations and tools such as Biblical-language dictionaries and concordances that will help you understand how potentially-confusing words are used elsewhere in scripture.

Scripture interprets scripture

Don't rely on trying to understand a single verse in isolation. Being familiar with the whole of scripture will help you to more naturally intuit what you read. When a particular verse troubles you, look around for other verses speaking on similar topics. Again, various tools such as study bibles and topical indices may be helpful.

Ask "experts"

While the above is definitely the best approach, it usually won't hurt to read what others have written, or to ask "subject matter experts". For example, you could ask here or on Hermeneutics.SE if a particular verse is perplexing you.

Ultimately, most people are not going to go to great lengths to do their own analysis; they are going to tend to lean on "experts" of a denomination familiar to them. The above is more a guide how to proceed if you either lack a church organization which you are predisposed to trust, or if, for whatever reason, your previously-existing trust is called into question.

You ask a good question—a really good one.

Let me start out with a question: What does "sola scriptura" mean?

Please bear with me for a moment as I get a little nit-picky. The three solā's are in the ablative case (in latin). They are tools, or instruments, or, to use the old Philosophical terminology, causes:

• Solā Gratiā: "By grace alone": The only motivation God would have to choose and save us is out of his undeserved love for us undeserving sinners.
• Solā Scripturā: "By scripture alone": The only instrument or tool that God uses to give forgiveness to us is his word.
• Solā Fide:. "by faith alone": The only instrument that passively receives this gift of salvation is faith.

The reason I mention this is that, already, out of the gate, the definition of "sola scriptura" has strayed to a different place than where it was hundreds of years ago among the reformers. Now it just, in an abstract way, in some circles, means: "Only God's word is true."

And now I can talk about the point of listing the three solas: How would you know this unless you had someone to teach you? You are off to a really good start. But you will have limited progress until you are able to sit down and be taught by someone who is faithful and competent to teach. As the Ethiopian Eunuch said:

“<30> Then Philip ran up to the chariot and heard the man reading Isaiah the prophet. “Do you understand what you are reading?” Philip asked. <31> “How can I,” he said, “unless someone explains it to me?” So he invited Philip to come up and sit with him.” (Acts 8:30–31 NIV11-GKE)

How then do you find that guy to teach you like the Ethiopian yearned to find? Here is my advice, for what it might be worth:

• Find someone trained in the Original languages. So much damage comes from those who are not trained well. We wouldn't let a nurse's aid do brain surgery. Yet, there are many who truly don't know how language works, let alone the Biblical languages. And yet people entrust their souls in their care.
• Look for a church body (not just an individual congregation) that has a record for thoroughly vetting prospective pastors and training them over the span of long years before they become pastors. Isolated, individual congregations have very little ability to train future pastors who are competent. And individual congregations have a repeated track-record of not being to hold their pastors accountable when their pastors err (in either doctrine or practice)
• Find a church that has a church year in place that seeks to preach "the whole will of God (Acts 20:27)". Too many churches focus on only a few, favorite sins, or even worse, the sins of those outside their congregation, or even worse still, the sins of joining an un-preferred political party. True churches expose a myriad of sins, since the scriptures do.
• Find a church that preaches the whole will of God. This is the other part of that task: A faithful church and pastor within that church will go out of his way to, unceasingly, and compassionately, in a myriad of different ways, show each of us how much Jesus cares for them and has paid for their sins. As an example of what to look for and what not to look for, I recommend watching this video: “The Gospel For Those Broken By The Church”. In the video, Dr. Rosenblatt does an amazing job of showing what happens when a pastor is either poorly trained, or misguided, and what to look for, both when you read God's word alone and also when you show up to church.

Please, let me say that I realize that I'm not answering all of your questions. And, I'm deliberately not answering all your questions. And the reason why is that I'm wondering if you're putting the cart before the horse. There is some use to reading the confessional statements of church bodies. But there's a reason why John says, “test the spirits” (1 John 4:1 NIV-GK). There's a reason why Jesus says, “Thus, by their fruit you will recognize them.” (Matt. 7:20 NIV-GK). You can do some homework ahead of time. But, it's best to sit down and talk to the pastor and test him based on what God's word says. But the reason I have listed the bullet points above is to give a pathway to chip away at that goal. It's not a 'to-do' list.

Finally, in full humility and honesty, let me also say that in all of what I have written here, I'm very and unabashedly biased. And as people have walked through classes to learn about my church, there has been this spiritual barnacle-scraping that takes place. It's uncomfortable to be taught one thing, in some cases, for decades, and then have a new guy say, "that's not how the Bible speaks." But, looking back, I was ever-so thankful to spend the long months teaching them. For slowly, over the long span of time, they learned to trust God's word. And as they learned to trust God's word, the doubt that comes along with being a sinner/saint stayed. But the doubt in figuring out what God's word said and meant slowly faded away.

May our good and gracious Lord bless you in your efforts.

First, we need to understand what sola scriptura is and is not. It is the belief that the Bible contains all that is necessary for salvific purposes, that the Bible is the sole infallible source of authority for Christian faith and practice.

Second, we need to clear up two misconceptions.

The first misconception is the assumption that it grew out from the Reformation that it was a reaction to the perception that the Roman Catholic Church had far exceeded what the Bible and apostles had revealed about Christian faith and practice. If a religion posits something it says is necessary for your salvation, but that it is not clear from the bible, then it may be rejected as unauthoritative regardless of who says it.

Instead, this belief has been around from the beginning of the Christian era. Irenaeus calls the Bible the ground and pillar of our faith.

1. We have learned from none others the plan of our salvation, than from those through whom the Gospel has come down to us, which they did at one time proclaim in public, and, at a later period, by the will of God, handed down to us in the Scriptures, to be the ground and pillar of our faith. Against Heresies Book III Chapter 1

The second misconception is the idea that only Protestants must deal with the question. The OP question about a Protestant interpreting the bible, but this is exactly the same as one might ask about interpreting Tradition (capitalized). After all, Catholic and Orthodox do not understand the same Tradition, although both claim it. The well-known filioque question is an example and there are many others, not the least of which is the Pope’s claimed authority.

It is a good, difficult question to answer. We all, of course, believe our interpretation of the Bible and Tradition are accurate. Is there anything that might help in our pursuit?

With that understanding in mind, the natural question would arise, how does one choose the correct interpretation of the Bible?

The answer is to recognize that sola scriptura still relies on Christian history, tradition, the church, the councils, and even your pastor. But sola scriptura asserts that all of those things are subject to the Bible.

Let’s look first at some easy examples of this in action.

Should your pope, priest, or pastor assert that Jesus was a man only, that there was a time when He was not, that He is created, you know that is false based on history, tradition, and the church, of which those things are based on the Bible.

And we know that the Son of God [Jesus Christ] is come, and hath given us an understanding, that we may know him that is true, and we are in him that is true, even in his Son Jesus Christ. This is the true God, and eternal life. 1 John 5:20

Should your pope, priest, or pastor assert that the mother Mary must be worshipped as a god in order for you to be saved, you know that is false based on history, tradition, and the church, of which those things are based on the Bible.

For thou shalt worship no other god: for the LORD, whose name is Jealous, is a jealous God: Exo 34:14

What of some other harder questions? How do we know?

What of baptism? Is it for babies or for those who choose? Can one be saved apart from water baptism?

The answers would be found like the other questions. The answer would be based on history, tradition, and the church, of which those things are and must be based on the Bible, else man’s opinion is substituted. It would not be based on “just so” answers of a presumed or even duly elected authority.

For example, there is Justin Martyr writing about the children of ignorance at their birth and the children of choice and knowledge. He cites the apostolic biblical teaching. See here.

As well, it helps to understand the motives behind certain doctrines. Is it for power, prestige, the pocketbook that some teach certain ideas that do not source to the Bible?

Further, like the ancients, one may ask when a doctrine is first espoused. Does it source to apostles or to those who claim to have a physical lineage of sorts to apostles? Like Irenaeus, we may reject those doctrines that came after the apostolic age.

What of communion? Is it a represented sacrifice or a memorial? Does it require a duly constituted priest or may any believer offer? Again, the answers would be based on Christian history, like from the earliest commentators who wrote within the first 200 years of Christ walking the earth. These would also cite the Bible as their authority. Paul speaks to brethren about communion, not to a separate class of priests.

Now I praise you, brethren, that ye remember me in all things, and keep the ordinances, as I delivered them to you. For I have received of the Lord that which also I delivered unto you, That the Lord Jesus the same night in which he was betrayed took bread: 1 Cor 11:2, 23

God wants a relationship with you directly. He is not offended by questions.

On the real-life example of a high profile married couple shifting churches, it doesn’t appear to be about sola scriptura as it was more about keeping the familial peace.

On the general divorce issue of different faiths marrying, this too doesn’t appear to be about sola scriptura, of finding true doctrine, as it was about unresolved conflict that married anyway. Generally speaking, however, if your spouse says the Holy Spirit said this and confirmed it by Scripture, then what will you do? People attend church for all types of reasons.

So, no, the believer wondering about the “correct” interpretation of Scripture, does not rely solely on self, but rather, on the Holy Spirit, on the church, on tradition, on councils, and on early Christian writers. All of whom relied on the Bible.

It’s like a string of pearls where the string is the Bible and the pearls are the church, tradition, councils, early Christian writers and the clasp keeping it all together is the Holy Spirit.

And frankly, this is what the Reformation was all about. Scripture is the sole authority from which to draw doctrine. This is what they did and from where the church had begun before, over the decades, descending into power struggles, prestige machinations, and pocketbook desires.

Despite the best answer having been chosen, I feel constrained to add three points in the Bible itself, addressed to Christians.

First of all, Protestantism is not a free-for-all, with each Protestant free to do his or her own thing, based on his or her own conclusions about the 'correct' interpretation of any Bible verses. Tragically, this is what it seems to be degenerating into in some quarters, due to forgetting these three Bible points.

1. Acts 2:42 - "And they continued steadfastly in the apostles' doctrine and fellowship, and in breaking of bread, and in prayers."

2. Jude vss. 3-4 - "Beloved, when I gave all diligence to write unto you of the common salvation, it was needful for me to write unto you, and exhort you that ye should earnestly contend for the faith which was once delivered unto the saints. For there are certain men crept in unawares, who were before of old ordained to this condemnation, ungodly men, turning the grace of our God into lasciviousness, and denying the only Lord God, and our Lord Jesus Christ."

3. 2 Cor. 11:2-4 - "For I have espoused you to one husband, that I may present you as a chaste virgin to Christ. But I fear, lest by any means, as the serpent beguiled Eve through his subtilty, so your minds should be corrupted from the simplicity that is in Christ. For if he that cometh preacheth another Jesus, whom we have not preached, or if ye receive another spirit, which ye have not received, or another gospel, which ye have not accepted, you might well bear with him... For such are false apostles, deceitful workers, transforming themseleves into the apostles of Christ. And no marvel, for Satan himself is transformed into an angel of light. Therefore it is no great thing if his ministers also be transformed as the ministers of righteousness; whose end shall be according to their works."

Only when Christians take their eyes off following their Lord by looking to what other men (or women) say about their Lord will confusion arise. Christians are told to stick to the first century apostolic teaching, all of which is in the scriptures. The 'simplicity' of what was taught back then was not simple teaching. James points out that the apostle Paul taught "some things hard to be understood, which they that are unlearned and unstable wrest, as they do also the other scriptures, unto their own destruction" (2 Peter 3:16). The "simplicity that is in Christ" is the one, sure means of not being lured away from following him due to attraction to the teaching of others, who claim to be able to explain to us what this, that, and the next biblical point means. Christians simply follow Christ; not this man, or that woman, or this denomination, or that creed.

Time and again we hear of Christian teachers and leaders being exposed as sexual predators, or of secretly indulging in p**nography, or stealing large sums of money from their ministries, or of being two-faced (lovely people in public, but monsters in their own households). Some were so practiced in their hypocrisy, it was not discovered until after they had died. Others committed suicide when their duplicitous way of life was discovered. In this day and age, Christians have seen time and again the danger of being so enamoured of any individual's teaching or ministry that they start following them. Yet that is what is happening on a massive scale!

What on earth happened so as to make us forget to "lay aside every weight, and the sin which doth so easily beset us, and let us run with patience the race that is set before us, looking unto Jesus the author and finisher of our faith"? (Hebrews 12:1-2) That is the simplicity that is in Christ.

Oh, but in this era of cult personality, and super-stars, and 'heroes', our eyes are attracted all over the place to this, that and the next person on a podium, when we should be looking only to Jesus, listening only to the first-century apostolic teaching, and saturating ourselves in scripture reading so that we are crystal-clear as to the biblical gospel, and the biblical Christ. He is the only foundation upon which Christians can stand - all other ground is sinking sand.

Proponents of Jesus Christ see and follow him alone (Sola Christos) which is entirely a sound Sola Scriptura principle. Keep that basic principle to the fore, and all the other problems you mentions should not trip you up.