From Luther's Heidelberg Disputation wherein he begins to give shape to his Theology of the Cross:
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].
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 theologian of glory calls evil good and good evil. A theologian of the cross calls the thing what it actually is.
22. That wisdom which sees the invisible things of God in works as perceived by man is completely puffed up, blinded, and hardened.
Happy Reformation Day!