The cross is revelation.
It does not reveal any particular thing, but God and man. It reveals who God is and who man is.
There is a curious presentiment of this situation in Greek philosophy: Plato's image of the crucified "just man".
In the Republic the great philosopher asks what is likely to be the position of a completely just man in this world. He comes to the conclusion that a man's righteousness is only complete and guaranteed when he takes on the appearance of unrighteousness, for only then is it clear that he does not follow the opinion of men but pursues justice only for its own sake.
So according to Plato the truly just man must be misunderstood and persecuted in this world; indeed, Plato goes so far as to write:
"They will say that our just man will be scourged, racked, fettered, will have his eyes burnt out, and at last, after all manner of suffering, will be crucified..." Republic, Book II, 361e-362a.
Joseph Cardinal Ratzinger, Introduction to Christianity, Herder and Herder: New York, 1970, p. 222.