I think today's Calvin and Hobbes cartoon illustrates a great deal of what Martin Luther was trying to say in his Heidelberg Disputation, but says it in a lot simpler terms.
If you want the longer version, I highly recommend two books. The first is the classic by Gerhard Forde, On Being a Theologian of the Cross. The second is Alistair McGrath's look at the same material, Luther's Theology of the Cross.
I'm planning to re-read Forde's book, as it is one that can't be absorbed fully on the first (or likely the second or third) reading.
I'm working on McGrath's book now. Good stuff. But Calvin (the kid, not the theologian) says it pretty well above.