Thoughts on Westminster Confession of Faith, articles I.9-10, which you can find here.
Our final appeal in debating and interpreting the Bible is to the original text. We interpret Scripture by Scripture. The highest standard and rule we have is the Bible, not the church or our reason. This is a weakness we have today. When we run into a question or problem in the Bible, our tendency is to consult our study Bible, or favorite online teacher, or commentary, or book, or the church fathers, etc. These can help, but the ultimate authority on the Bible is the Bible. If the Bible is hard to understand on Levitical laws and sacrifices, there are other places that more clearly explain what it was all about (Hebrews). If we aren’t sure if a character in a story is doing the right thing, there are verses elsewhere that teach ethically if he is being faithful or not.
The confession makes a side comment that the meaning of Scripture is singular, not manifold. This was a rejection of the medieval system of finding four meanings in every text. Some misinterpret this and assert that there is only one application of any text, or only one right way to articulate and summarize a text. No, there is one basic sense of the passage, which can (and should) be stated variously, and applied in several ways.
The confession is often enlightening when you take out all the subordinate clauses. “The supreme judge… [is] the Holy Spirit speaking in the Scripture.” Note the pointer not to the Bible ultimately, not even to Jesus, ultimately, but to the Spirit, whom Jesus has poured out upon us to lead us into all truth.