How to do theology

A seminal quote from Luther's Heidelberg Disputation:

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.

Thanks Mark B.