I wish that all the pieces of my theology fit together seamlessly like the pieces of a jigsaw puzzle. When I gain an insight from the Bible or change my understanding of what a portion of the Bible means, I want to fit that understanding into the "big picture." How does my new insight fit into the rest of the pieces that I have assembled in my head?
Unfortunately, not everything fits neatly. I find gaps or overlaps in the picture. The pieces don't always fit where I think they should. I could take a hammer and pound the new piece into place, but I would wind up damaging something important in the process.
I think I expect too much.
Part of it is me. My little brain can't take it all in.
Part of it is the text itself. Some would have us see the Bible as one monolithic document; if we could only understand it correctly, the picture it would paint would be complete and internally consistent. But the Bible is not one document; it is a library. God has chosen to make himself known in a library of documents of varying genre, written in different ages for different purposes. (See God's Bookshelf)
Asking how to make the pieces to fit together seamlessly is like asking to where the pickle fits when you're building a bicycle.
There is a unity to the scriptures, but it is not the simple unity of pieces that fit together like parts of a machine. It's the kind of unity that an artist can perhaps appreciate more than an engineer.
And if we're going to use metaphors from the art world to understand God's self-revelation in the scriptures, we should probably think more along the lines of sculpture than of painting. That is, we should think in three dimensions, not two.
To understand a three-dimensional work of art, you have to look at from all sides. The same sculpture can look very different when you walk around it and change your point of view. Similarly, the various components of the canonical scriptures give us insight into God from a number of different perspectives. We need them all to get the whole picture.
Related follow-up: Rule of Faith