A quote from Bernard Ramm, Protestant Biblical Interpretation (Baker, 1970), on Luther’s interpretive method (pg. 55-56):
The competent Christian was sufficient to interpret the Bible, and the Bible is sufficiently clear in content to yield its meaning to the believer. Further, the Bible was a world of fits own and so Scripture interprets Scripture. At point where the Bible was obscure, the Catholic referred to the unwritten tradition of the Church. But Luther shut the interpreter up within the Bible and made the obscure passage yield to a clear passage. Much of Catholic exegesis was nothing more than studies in patristics. This Luther rejected:
I ask for Scriptures and Eck offers me the Fathers. I ask for the sun and he gives me his lanterns. I ask: “Where is your Scripture proof?” and he adduces Ambrose and Cyril… With all due respect to the Fathers I prefer the authority of Scripture.
A corollary at this point is: the analogy of faith. The scholastics interpreted by glosses and catena of citations from the Fathers. This was arbitrary and disconnected. Luther insisted on the organic, theological unity of the Bible. All of the relevant material on a given subject was to be collected together so that the pattern of divine revelation concerning that subject would be apparent.