D. A. Carson, “Unity and Diversity in the New Testament: The Possibility of Systematic Theology,” in Scripture and Truth (ed. D. A. Carson and John D. Woodbridge; Grand Rapids: Zondervan, 1983), 81–82:

I am not saying that the Bible is like a jigsaw puzzle of five thousand pieces and that all the five thousand pieces are provided, so that with time and thought the entire picture may be completed. Rather, I am suggesting that the Bible is like a jigsaw puzzle that provides five thousand pieces along with the assurance that these pieces all belong to the same puzzle, even though ninety-five thousand pieces (the relative figures are unimportant for my analogy) are missing. Most of the pieces that are provided, the instructions insist, fit together rather nicely; but there are a lot of gaping holes, a lot of edges that cry out to be completed, and some clusters of pieces that seem to be on their own. Nevertheless, the assurance that all of the pieces do belong to one puzzle is helpful, for that makes it possible to develop the systematic theology, even though the systematic theology is not going to be completed until we receive more pieces from the One who made it. And meanwhile, even some systematicians who believe that all the pieces belong to the same puzzle are not very adept puzzle players but sometimes force pieces into slots where they don’t really belong. The picture gets distorted somewhat, but it remains basically recognizable.