Luther, The Heidelberg Disputation, 26 April 1518:
19. That person does not deserve to be called a theologian who looks upon the »invisible« things of God as though they were clearly »perceptible in those things which have actually happened« (Rom. 1:20; cf. 1 Cor 1:21-25).
20. He deserves to be called a theologian, however, who comprehends the visible and manifest things of God seen through suffering and the cross.
21. A theology of glory calls evil good and good evil. A theology of the cross calls the thing what it actually is.
This is clear: He who does not know Christ does not know God hidden in suffering. Therefore he prefers ,works to suffering, glory to the cross, strength to weakness, wisdom to folly, and, in general, good to evil. These are the people whom the apostle calls »enemies of the cross of Christ« (Phil. 3:18), for they hate the cross and suffering and love works and the glory of works. Thus they call the good of the cross evil and the evil of a deed good. God can be found only in suffering and the cross, as has already been said Therefore the friends of the cross say that the cross is good and works are evil, for through the cross works are dethroned and the »old Adam«, who is especially edified by works, is crucified. It is impossible for a person not to be puffed up by his »good works« unless he has first been deflated and destroyed by suffering and evil until he knows that he is worthless and that his works are not his but God’s.