Are all doctrines equal? Or are some primary and others secondary?

As I'm going through the online lessons at Ligonier Connect, the second lesson in the course "Principles of Biblical Interpretation" opens with the teacher, RC Sproul, asking his audience if, after sharing an interpretation of scripture with a person they have ever been confronted with the rejoinder "That’s your interpretation!" Sometimes the person means to give a subtle (or not so subtle) rejoinder that really means, 'You're wrong!' Most often it can mean that the person believes that there are multiple ways to interpret a specific verse or passage of scripture.

There aren't.

Did you know that the Author of the Bible intended only ONE meaning for each and every passage of Scripture? There is only one way to interpret it and be correct. There are multiple ways to apply the verse, but only one meaning the Author intended.

For example, we know that God is three-in-one. If a person says "I interpret 1 John 5:7-8 as God being three persons in one Being" and the other person says, "No, I interpret that verse as God being only one being but three personalities at any given time," one of these people would be wrong. One person says you should be baptized by sprinkling and another says you should be baptized by immersion, one of those people are going to be wrong because they are opposite actions. One person says the rapture will come before the Tribulation and the next person says that the rapture will come after the tribulation...well one of those is wrong. They are not both right. Contradictions mutually exclude each other.

Scripture cannot contradict itself.

Sproul said,
The right of private interpretation carries with it the responsibility of correct interpretation. Our interpretation must always be monitored and compared to the collective wisdom of others.
Now, knowing that there is only one correct interpretation of scripture puts more light on the Author than it does on the interpreter, hopefully. We know He intended one meaning. But He is God, and we are not. Because we are sinful human beings, we must approach the interpretation of the scriptures humbly. We use a systematic theology, not Bible Dip, do not strip away the context, we're not helter skelter or haphazard about it. As noted above, the privilege of being given God's word comes with it a responsibility to interpret it correctly.

Relying on the collective wisdom of others is also a good idea. God raised up men and women in previous generations who taught, wrote, and interpreted in ways that have remained and remained for a reason. Their works come to us in these newer generations. This is important- it's not 'cheating' to use commentaries or theological tomes of yore that add to our wisdom. We don't use them to the exclusion of the Bible, but as a supporting method. Secondly, since we do rely on the collective wisdom of others in learning the historic faith, we do not go after the lone outlier who says "I have a new way!' Or, "I cracked a code no one has ever noticed before!" When the canon closed, so did the availability to interpret wildly new things from it that very from the historical faith.

But even if we or an angel from heaven should preach to you a gospel contrary to the one we preached to you, let him be accursed. (Galatians 1:8).

Thirdly, there are some doctrines with which we must have a settled conviction and do not compromise. These are known as the primary essentials. They are primary because they are salvific. They are essential because the Bible declares them so. Scripture on this point must be interpreted and held dearly among those of the truth faith. These foundational tenets comprise the historical faith.

Other, secondary matters (non-salvific) interpreted differently between two people don't have to mean that one breaks fellowship over them. If one says baptism is sprinkling and the other says baptism is immersion, well, what they are both saying is they agree that the Bible does present an ordinance of baptism. That much is clear. They just differ on how.

Here is a good link explaining primary essential doctrines. They both are to Christian Apologetics and Research Ministry, (CARM). This first one is a visual doctrine grid. This one is to an essay explaining each essential doctrine and why they are essential.

Alternately, back when he was a PyroManiac, Phil Johnson wrote about why the distinction between essential and peripheral is doctrines so crucial. He wrote again on how the Bible itself teaches us how to distinguish between primary and peripheral doctrines. Pastor Johnson concluded his essay by saying,
I'm as eager to see evangelical unity as I am to attack ecumenical compromise. But in order to keep the two straight, it is crucial to have clear biblical reasons for treating various doctrines as either fundamental or secondary.
Hence, this post and the links to good resources on the subject.

Happy studying :)