The crucified Son of God is the historic event upon which every attempt of the mind to construct an adequate explanation of the meaning of existence upon merely human argumentation comes to grief. The true key-point, which challenges every philosophy, is Jesus Christ's death on the Cross. It is here that every attempt to reduce the Father's saving plan to purely human logic is doomed to failure.
“Where is the one who is wise? Where is the learned? Where is the debater of this age? Has not God made foolish the wisdom of the world?” (1 Cor 1:20), the Apostle asks emphatically. The wisdom of the wise is no longer enough for what God wants to accomplish; what is required is a decisive step towards welcoming something radically new: “God chose what is foolish in the world to shame the wise...; God chose what is low and despised in the world, things that are not to reduce to nothing things that are” (1 Cor 1:27-28). Human wisdom refuses to see in its own weakness the possibility of its strength; yet Saint Paul is quick to affirm: “When I am weak, then I am strong” (2 Cor 12:10). Man cannot grasp how death could be the source of life and love; yet to reveal the mystery of his saving plan God has chosen precisely that which reason considers “foolishness” and a “scandal”. Adopting the language of the philosophers of his time, Paul comes to the summit of his teaching as he speaks the paradox: “God has chosen in the world... that which is nothing to reduce to nothing things that are” (cf. 1 Cor 1:28). In order to express the gratuitous nature of the love revealed in the Cross of Christ, the Apostle is not afraid to use the most radical language of the philosophers in their thinking about God. Reason cannot eliminate the mystery of love which the Cross represents, while the Cross can give to reason the ultimate answer which it seeks. It is not the wisdom of words, but the Word of Wisdom which Saint Paul offers as the criterion of both truth and salvation. The wisdom of the Cross, therefore, breaks free of all cultural limitations which seek to contain it and insists upon an openness to the universality of the truth which it bears. What a challenge this is to our reason, and how great the gain for reason if it yields to this wisdom! Of itself, philosophy is able to recognize the human being's ceaselessly self-transcendent orientation towards the truth; and, with the assistance of faith, it is capable of accepting the “foolishness” of the Cross as the authentic critique of those who delude themselves that they possess the truth, when in fact they run it aground on the shoals of a system of their own devising.
-Pope John Paul II, Fides et Ratio