While the truth of the scripture is guaranteed by its author, not all truths are found in scripture. I might know that Jesus is God because the Bible tells me, but I am pretty sure the Bible tells me nothing about algebra or the chemical composition of water. This is an important fact because a hermeneutic is developed partly prior to reading the Bible. A hermeneutic is a method of interpretation. We all develop a hermeneutic based on our intellectual faculties, background information, and skills. And we do so whether we are conscious of it or not. A good hermeneutic will enable us to get the right interpretation of the texts we study. And most of us, at least initially, develop our hermeneutic without the Bible. In fact, some people don't read the Bible until later in life. They have already worked out how to interpret the world almost entirely without reference to the Bible.
But, and here's the problem, if our hermeneutic is developed before reading the Bible, how do we know if we have the right hermeneutic for interpreting the Bible itself? And if we don't have the right hermeneutic won't that mean we won't interpret scripture correctly?
The Bible is foundational to all human knowledge, because it is the revealed Word of God who is the source of all knowledge (Proverbs 1:7; Colossians 2:3). This doesn't mean that all truth is found in scripture. But it does mean that all scripture is true (John 17:17; 2 Timothy 3:16-17). And the truth of scripture frames the basic worldview that is necessary in order for us to discover the truth of anything else... Hermeneutical principles, laws of logic, orderliness in nature, standards of morality, and all other aspects of knowledge have their foundation in the truth of scripture (Jason Lisle, Understanding Genesis, 166).
The implication of Lisle’s argument is that it is in virtue of the truth of scripture that human beings are able to understand scripture before they have read it. If scripture was not true, then human beings would not be able to understand it and, furthermore, they would not be able to understand anything else.
Jason Lisle, Understanding Genesis (Green Forest, AR: Master Books, 2015).