That question was put to then-Cardinal Joseph Ratzinger by Peter Seewald in the interview that became the wonderful book, God and the World: A Conversation with Peter Seewald (Ignatius Press, 2002):
Seewald: What would actually have happened if Christ had not appeared and if he had not died on the tree of the Cross? Would the world long since have come to ruin without him?
Cardinal Ratzinger: That we cannot say. Yet we can say that man would have no access to God. He would then only be able to relate to God in occasional fragmentary attempts. And, in the end, he would not know who or what God actually is.
Something of the light of God shines through in the great religions of the world, of course, and yet they remain a matter of fragments and questions. But if the question about God finds no answer, if the road to him is blocked, if there is no forgiveness, which can only come with the authority of God himself, then human life is nothing but a meaningless experiment. Thus, God himself has parted the clouds at a certain point. He has turned on the light and has shown us the way that is the truth, that makes it possible for us to live and that is life itself.
Seewald: Someone like Jesus inevitably attracts an enormous amount of attention and would be bound to offend any society. At the time of his appearance, the prophet from Nazareth was not only cheered, but also mocked and persecuted. The representatives of the established order saw in Jesus' teaching and his person a serious threat to their power, and Pharisees and high priests began to seek to take his life. At the same time, the Passion was obviously part and parcel of his message, since Christ himself began to prepare his disciples for his suffering and death. In two days, he declared at the beginning of the feast of Passover, "the Son of Man will be betrayed and crucified."
Cardinal Ratzinger: Jesus is adjusting the ideas of the disciples to the fact that the Messiah is not appearing as the Savior or the glorious powerful hero to restore the renown of Israel as a powerful state, as of old. He doesn't even call himself Messiah, but Son of Man. His way, quite to the contrary, lies in powerlessness and in suffering death, betrayed to the heathen, as he says, and brought by the heathen to the Cross. The disciples would have to learn that the kingdom of God comes into the world in that way, and in no other.
Read more of the interview on Ignatius Insight: