And then I read Trevor McIlwain's wonderful Building on Firm Foundations, Volume I: Guidelines for Evangelism and Teaching Believers (New Tribes Mission, 5th edition, 1991). Here's how he explains, on pages 112-113, the mechanism of God's progressive revelation:
"God's basic method of teaching can be likened to the way an artist paints a picture. An artist does not begin painting in one corner of the canvas and immediately complete every detail. Instead, he will often do an initial, simple, light sketch of the whole picture. To an onlooker, the picture in the early stages will be indistinct. Even when studied, it may not be clear just what the artist intends to include in the final product. But, as the artist continues to work on the picture, here a little and there a little, the details begin to develop with greater clarity. This process continues until the final strokes are applied and the picture is complete.
"This is how God painted His picture of the drama of redemption. He began the sketch in the early chapters of Genesis. Genesis 3:15 is a simple, undetailed sketch of the whole picture of the redemption story. Sharper, clearer details were then added by God in the call and life of Abraham. More color and features were put onto the canvas in the offering of Isaac and the perfect lamb substitute which God provided. Jacob's dream, the Passover, the manna from Heaven, the water from the smitten rock, the giving of the Law, the building of the Tabernacle, the brazen serpent, Joshua's victorious ministry, and other historical events are all strokes of the Artist's brush as He painted the background of the picture.
"The Master Painter continued adding details as He guided the events of Old Testament history toward the revelation of Christ, the main subject of the painting. Obscure images and lightly sketched areas suddenly emerged when Jesus came to live, die and rise again. But even then, the canvas did not contain the whole picture. Through the apostles, the Holy Spirit continued the painting. The final strokes to God's picture were made when the revelation of Jesus Christ, given to John on the Isle of Patmos, was added.
"God never taught all there was to know about any particular doctrine or subject at one specific time. He often revealed some new area of truth, but He never immediately gave the whole truth regarding any one subject."
So the next time someone informs you that "judge not" means we are not to disrespect someone else's imaginative-but-heartfelt ideas about God, or that "God so loved the world" means everyone is going to heaven except Hitler, try using this metaphor. Then invite him or her to try understanding Michelangelo's Sistine Chapel simply by glancing at Adam's thumbnail.