When I read the question about Adam and Eve I thought about the Exultet the Church proclaims during the Easter Vigil, specifically the line, "O happy Fault, O sin of Adam that brought to us such a great Redeemer." From what I can best interpret from this line, the sin of Adam and Eve is what brought the wheels in motion for our Savior.
Had Adam and Eve not sinned, would we have not then had Jesus?
Answer by Richard Geraghty on 10/28/2007:
St. Thomas maintains that all we know for sure is the revelation that Christ came down to earth to save us from our sins. As far as we known, then, he most likely would not have become a human being if Adam and Eve had stayed the way they were supposed to be. But they sinned, apparently ruining the plan of God for them. But God brought good out of this evil by becoming a man, as you pointed out in the prayer of the Exultet. There are Franciscan theologians, however, who hold that God would have become a man even if Adam and Eve had not sinned. This is the less common view.