It has often been charged that the Bible can't be trusted because people can make it say anything they want it to say. This charge would be true if the Bible were not the objective Word of God, if it were simply a wax nose, able to be shaped, twisted, and distorted to teach one's own precepts. The charge would be true if it were not an offense to God the Holy Spirit to read into sacred Scripture what is not there. However, the idea that the Bible can teach anything we want it to is not true if we approach the Scriptures humbly, trying to hear what the Bible says for itself.
Sometimes systematic theology is rejected because it is seen as an unwarranted imposition of a philosophical system on the Scriptures. It is seen as a preconceived system, a Procrustean bed into which the Scriptures must be forced by hacking off limbs and appendages to make it fit. However, the appropriate approach to systematic theology recognizes that the Bible itself contains a system of truth, and it is the task of the theologian not to impose a system upon the Bible, but to build a theology by understanding the system that the Bible teaches.
At the time of the Reformation, to stop unbridled, speculative, and fanciful interpretations of Scripture, the Reformers set forth the fundamental axiom that should govern all biblical interpretation. It is called the analogy of faith, which basically means that Holy Scripture is its own interpreter. In other words, we are to interpret Scripture according to Scripture. That is, the supreme arbiter in interpreting the meaning of a particular verse in Scripture is the overall teaching of the Bible.
Behind the principle of the analogy of faith is the prior confidence that the Bible is the inspired Word of God. If it is the Word of God, it must therefore be consistent and coherent. Cynics, however, say that consistency is the hobgoblin of little minds. If that were true, then we would have to say that the smallest mind of all is the mind of God. But there is nothing inherently small or weak to be found in consistency. If it is the Word of God, one may justly expect the entire Bible to be coherent, intelligible, and unified. Our assumption is that God, because of His omniscience, would never be guilty of contradicting Himself. It is therefore slanderous to the Holy Spirit to choose an interpretation of a particular passage that unnecessarily brings that passage into conflict with that which He has revealed elsewhere. So the governing principle of Reformed hermeneutics or interpretation is the analogy of faith.
A second principle that governs an objective interpretation of Scripture is called the sensus literalis. Many times people have said to me, incredulously, "You don't interpret the Bible literally, do you?" I never answer the question by saying, "Yes," nor do I ever answer the question by saying, "No." I always answer the question by saying, "Of course, what other way is there to interpret the Bible?" What is meant by sensus literalis is not that every text in the Scriptures is given a "woodenly literal" interpretation, but rather that we must interpret the Bible in the sense in which it is written. Parables are interpreted as parables, symbols as symbols, poetry as poetry, didactic literature as didactic literature, historical narrative as historical narrative, occasional letters as occasional letters. That principle of literal interpretation is the same principle we use to interpret any written source responsibly.
The principle of literal interpretation gives us another rule, namely that the Bible in one sense is to be read like any other book. Though the Bible is not like any other book in that it carries with it the authority of divine inspiration, nevertheless, the inspiration of the Holy Spirit over a written text does not turn verbs into nouns or nouns into verbs. No special, secret, arcane, esoteric meaning is poured into a text simply because it's divinely inspired. Nor is there any such mystical ability we call "Holy Ghost Greek." No, the Bible is to be interpreted according to the ordinary rules of language.
Closely related to this point is the principle that the implicit must be interpreted by the explicit, rather than the explicit interpreted by the implicit. This particular rule of interpretation is violated constantly. For example, we read in John 3:16 that "whoever believes in him should not perish but have eternal life," and many of us conclude that since the Bible teaches that anyone who believes shall be saved, it therefore implies that anyone can, without the prior regenerative work of the Holy Spirit, exercise belief. That is, since the call to believe is given to everyone, it implies that everyone has the natural ability to fulfill the call. Yet the same gospel writer has Jesus explaining to us three chapters later that no one can come to Jesus unless it is given to him of the Father (6:65). That is, our moral ability to come to Christ is explicitly and specifically taught to be lacking apart from the sovereign grace of God. Therefore, all of the implications that suggest otherwise must be subsumed under the explicit teaching, rather than forcing the explicit teaching into conformity to implications that we draw from the text.
Finally, it is always important to interpret obscure passages by those that are clear. Though we affirm the basic clarity of sacred Scripture, we do not at the same time say that all passages are equally clear. Numerous heresies have developed when people have forced conformity to the obscure passages rather than to the clear passages, distorting the whole message of Scripture. If something is unclear in one part of Scripture, it probably is made clear elsewhere in Scripture. When we have two passages in Scripture that we can interpret in various ways, we want always to interpret the Bible in such a way as to not violate the basic principle of Scripture's unity and integrity.
These are simply a few of the basic, practical principles of biblical interpretation that I set forth years ago in my book Knowing Scripture. I mention that here because so many people have expressed to me how helpful it has been to guide them into a responsible practice of biblical interpretation. Learning the principles of interpretation is exceedingly helpful to guide us in our own study.