If we are to believe he is really alive with all that that implies, then we have to believe without proof. And of course that is the only way it could be. If it could be somehow proved, then we would have no choice but to believe. We would lose our freedom not to believe. And in the very moment that we lost that freedom, we would cease to be human beings. Our love of God would have been forced upon us, and love that is forced is of course not love at all. Love must be freely given. Love must live in the freedom not to love; it must take risks. Love must be prepared to suffer even as Jesus on the Cross suffered, and part of that suffering is doubt.