I wrote my doctoral thesis on the value of various philosophical arguments that try to prove the existence of God. Can there be such a proof? Brilliant philosophers, from Anselm, through Aquinas, through Descartes, through contemporary intellectuals like Charles Hartshorne, submit that the existence of God can be proven through rational argument. Except, except, a lot depends upon what exactly we mean by the word "prove". How do we prove something?
There's a legend about St. Christopher that's pertinent here: Christopher was a man gifted in every way, except faith. He was physically strong, powerful, goodhearted, mellow, and well liked. He was also generous, using his physical strength to help others, but he found it hard to believe in God, even though he wanted to. For him, the physical was what was real and everything else seemed unreal. And so, as the legend goes, he lived his life in a certain honest agnosticism, unable to really believe in anything beyond what he could physically see, feel, and touch.
However, this did not prevent him from using his gifts, especially his physical strength, to serve others. This was his refuge, generosity and service. He became a ferryboat operator, spending his life helping to carry people across a dangerous river. One night, as the legend goes, during a storm, the ferryboat capsized and Christopher dove into the dark waters to rescue a young child. Carrying that child to the shore, he looked into its face and saw there the face of Christ. After that, he believed for he had seen the face of Christ.
For all its piety, this legend contains a profound lesson. It changes the perspective on the question of how one tries to "prove" God's existence. Our attempt to prove God's existence has to be practical, existential, and incarnate rather than mainly intellectual. How do we move from believing only in the physical, from believing only in the reality of what we can see, feel, touch, taste, and smell, to believing in the existence of deeper, spiritual realities?
There's lesson in the Christopher story: Live as honestly and respectfully as you can and use your gifts to help others. God will appear. God is not found at the conclusion of a philosophical syllogism but as the result of a certain way of living. Moreover, faith is not so much a question of feeling as of selfless service.
There's a further lesson in the biblical account of the apostle, Thomas, and his doubt about the resurrection of Jesus. Remember his protest: "Unless I can (physically) place my finger in the wounds of his hands and stick my finger into the wound of his side, I will not believe." Note that Jesus offers no resistance or rebuke in the face of Thomas' skepticism. Instead, he takes Thomas at his word: "Come and (physically) place your finger in the wounds of my hand and the wound in my side; see for yourself that I am real and not a ghost."
That's the open challenge for us: "Come and see for yourselves that God is real and not a ghost!" That challenge, however, is not so much an intellectual one as a moral one, a challenge to be honest and generous.
Skepticism and agnosticism, even atheism, are not a problem as long as one is honest, non-rationalizing, non-lying, ready to efface oneself before reality as it appears, and generous in giving his or her life away in service. If these conditions are met, God, the author and source of all reality, eventually becomes sufficiently real, even to those who need physical proof. The stories of Christopher and Thomas teach us this and assure us that God is neither angered nor threatened by an honest agnosticism.
Faith is never certainty. Neither is it a sure feeling that God exists. Conversely, unbelief is not to be confused with the absence of the felt assurance that God exists. For everyone, there will be dark nights of the soul, silences of God, cold lonely seasons, skeptical times when God's reality cannot be consciously grasped or recognized. The history of faith, as witnessed by the life of Jesus and the lives of the saints, shows us that God often seems dead and, at those times, the reality of the empirical world can so overpower us that nothing seems real except what we can see and feel right now, not least our own pain.
Whenever this happens, like Christopher and Thomas, we need to become honest agnostics who use our goodness and God-given strengths to help carry others across the burdensome rivers of life. God does not ask us to have a faith that is certain, but a service that is generous and sustained. We have the assurance that should we faithfully help carry others, we will one day find ourselves before the reality of God who will gently say to us: "See for yourself, that I am real, and not a ghost."
Can we prove that God exists? In theory, no; in life, yes.