score:1
I'll offer a response in 2 parts:
A Latter-day Saint's perspective
It was a similar concern that led Joseph Smith to start asking questions that the ministers of his day could not answer. In his personal history he recorded some of his feelings as he lived through the Second Great Awakening:
8 During this time of great excitement my mind was called up to serious reflection and great uneasiness...so great were the confusion and strife among the different denominations, that it was impossible for a person young as I was, and so unacquainted with men and things, to come to any certain conclusion who was right and who was wrong.
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10 In the midst of this war of words and tumult of opinions, I often said to myself: What is to be done? Who of all these parties are right; or, are they all wrong together? If any one of them be right, which is it, and how shall I know it?
11 While I was laboring under the extreme difficulties caused by the contests of these parties of religionists, I was one day reading the Epistle of James, first chapter and fifth verse, which reads: If any of you lack wisdom, let him ask of God, that giveth to all men liberally, and upbraideth not; and it shall be given him.
12 Never did any passage of scripture come with more power to the heart of man than this did at this time to mine. It seemed to enter with great force into every feeling of my heart. I reflected on it again and again, knowing that if any person needed wisdom from God, I did; for how to act I did not know, and unless I could get more wisdom than I then had, I would never know; for the teachers of religion of the different sects understood the same passages of scripture so differently as to destroy all confidence in settling the question by an appeal to the Bible.
13 At length I came to the conclusion that I must either remain in darkness and confusion, or else I must do as James directs, that is, ask of God. I at length came to the determination to βask of God,β concluding that if he gave wisdom to them that lacked wisdom, and would give liberally, and not upbraid, I might venture. (Joseph Smith History)
Joseph Smith recognized that the same passages of scripture could be argued to support a wide diversity of doctrines. I believe this is, fundamentally, the same observation that stands behind the OP.
His response, inspired by the Biblical text, was to seek further guidance from God. The subsequent verses in his personal history describe his First Vision, and the resulting Restoration of many Gospel truths.
The experience of Joseph Smith demonstrates several additional sources that can help clarify Biblical passages that might otherwise be interpreted several different ways:
A historian's perspective
The degree to which we are dependent on non-Biblical sources in order to understand Biblical texts is difficult to overstate. We have a Strong's Concordance for Greek because of the millions of words preserved in pagan Greek writings. We understand the context of the ministry of the apostles because of the writings of Roman historians.
Second Temple Jewish history
The records of the culture, customs, and beliefs of the Jews, especially proximate to New Testament times, are a wealth of information regarding how the people who originally wrote & read the New Testament documents would have understood them (we have far fewer such records prior to the 2nd temple era).
In the context of the debate referenced in the OP, 2nd temple Jewish sources demonstrate a belief in post-mortal consciousness. The parable of the rich man & Lazarus in Luke 16 is an example of a teaching regarding post-mortality that is saturated with beliefs prevalent in contemporary Judaism.
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Early Patristic Writings
The writings of the Ante-Nicene Fathers represent an era when the church was not yet politically powerful. As a result, people who were already putting their lives on the line to practice their beliefs didn't have incentive to keep an Emperor (or any other political figure) happy by compromising on what they believed. These writers are within just a few generations of the apostles. They disagreed with each other all the time. But where there is a clear majority (and occasionally they're bordering on unanimous) view, this ought to be taken seriously. Did all of the disciples of all of the apostles completely lose the Gospel message that quickly? If so, why do we trust that they handed down the New Testament to us accurately?
In the context of the debate in the OP, the Ante-Nicene Fathers support post-mortal consciousness by a significant super-majority.
Conclusion
Although I take no issue generally with the idea that scripture interprets scripture, I suggest the maxim can be overdone if taken to an exclusionary extreme. All manner of sources enable us to understand scripture. We may not treat them all of these sources with the same level of authority or reliability, but we ignore them to our own loss.
A source I particularly treasure is modern revelation. I believe in a God who speaks in our time, to our knowledge base, and for our understanding. His revelation in the past is of inestimable value, but it was not fundamental to our salvation that we learn Hebrew, Greek, or history. I believe His ongoing revelation today is the most directly applicable resource for resolving ambiguity in ancient holy writ.
Upvote:2
This article on The Basics of Sound Biblical Interpretation puts the principle
Scripture interprets scripture and the less clear or plain passages of scripture MUST be interpreted in the light of the clearer passages
in its proper context within the modern hermeneutical method called Historical Grammatical which started in the 18th century 1:
Notes:
If after applying all the principles above, it's still not clear, then God simply didn't reveal enough and believers are given options.
Another way to supplement the above principles to come up with better guidance or additional teaching is by judiciously use Tradition, Reason, and Experience. Different theological tradition will do them differently; see Wikipedia article Prima Scriptura.
Bible study is supposed to be practical: there is sufficient revelation for entering into a Christian spiritual life and for journeying to heaven. In my opinion, a believer can then decide on his/her comfort level; if you need more certainty, join a denomination that can offer more teachings than the above principles can give you.
1 see "The Origins of Modern Hermeneutical Practices" section of Darren Slade's paper below