"It is a general maxim of hermeneutics that God's Word is to be found in the intent of scripture. This is an especially crucial matter to the hermeneutics of historical narratives. It is one thing for the historian to include an event because it serves the greater purpose of his work and yet another to thing for the interpreter to take that incident as having teaching value apart from the historian's larger intent... This does not mean that what is incidental is false, nor that it has no theological value; it does mean that God's Word for us for us in that narrative is primarily related to what it was intended to teach."
[From the oldie but goodie How to read the Bible for all it's worth by Fee and Stuart, 1982, p98-99. Although I see on Amazon there is now a 2003 edition available]