Geoff Wood writes that a stained glass illustrates the importance of the Old Testament:

High over the portals within the south transept of the 800-year-old cathedral of Chartres in France spreads a great Rose window, forty feet in diameter. At its center sits Christ, while immediately around him orbit eight angels and symbols for the four evangelists, each enclosed within a circle of stained glass-and beyond them orbit the 24 elders of the book of Revelation, each also within its own bejeweled circle—for a total of 36 orbiting circles of blue, red, gold, purple, and white! Enough to make your head spin. Nor is that gigantic wheel of color the only thing to enchant you in that soaring wing of the cathedral, because below it rise five more long and narrow windows, the central one featuring Mary, while the other four show images of the evangelists, Luke and Matthew, John, and Mark-in that sequence.

Now if you look closely at the windows for the four gospel writers, you'll notice something amusing. All four, appearing almost boyish in size, sits on the shoulders of a tall prophet of the Old Testament: Luke on the shoulders of Jeremiah, Matthew on Isaiah's, John on Ezekiel's, and Mark on Daniel's. The four major voices of the New Testament ride piggyback on the four major voices of the Old—just the way a dad might lift a small child on his shoulders. Why would those artists do something as playful as that? Well, it wasn't playful. They wanted to make a serious point, namely that the gospels build on the wisdom and vision of the Old Testament.