This graphic from The Guardian newspaper shows the cross-references present in our modern Bible. As much as anything else, the Bible is a conversation across the generations by authors who share a tradition.
The volume of internal references is surely what led the reformers to conclude that the meaning of Scripture could be gleaned by comparing less clear Scriptures to more clear:
All things in Scripture are not alike plain in themselves, nor alike clear unto all (2 Pet. 3:16); yet those things which are necessary to be known, believed, and observed for salvation, are so clearly propounded, and opened in some place of Scripture or other, that not only the learned, but the unlearned, in a due use of the ordinary means, may attain unto a sufficient understanding of them (Ps. 119:105, 130).
Westminster Confession of Faith (1.7)
But, if many things still remain abstruse to many, this does not arise from obscurity in the Scriptures, but from [our] own blindness or want [i.e. lack] of understanding, who do not go the way to see the all-perfect clearness of the truth… Let, therefore, wretched men cease to impute, with blasphemous perverseness, the darkness and obscurity of their own heart to the all-clear scriptures of God… If you speak of the internal clearness, no man sees one iota in the Scriptures, but he that hath the Spirit of God… If you speak of the external clearness, nothing whatever is left obscure or ambiguous; but all things that are in the Scriptures, are by the Word brought forth into the clearest light, and proclaimed to the whole world.
Martin Luther, Bondage of the Will
To begin with, it is important to note what the clarity of Scripture does not mean. It does not mean, first of all, that interpretation is unnecessary – the biblical meaning will be delivered up by some mystical process of hermeneutical osmosis. Nor does it mean that an autonomous individual can, by employing critical techniques alone, wrest the meaning from the text. Rather, clarity means that the Bible is sufficiently unambiguous in the main for any well-intentioned person with Christian faith to interpret each part with relative adequacy. In the context of the Reformation, the perspicuity of Scripture was the chief weapon for combating the authority of the dominant interpretive community: Rome (pg. 315).
Kevin J. VanhoozerIs There a Meaning in This Text?