Says who? Thats Paul's idea...which wasnt even established as an official pillar of catholicism until many centuries later when it became the 'doctrine of atonement'.
Jesus himself never said any such thing.
And its clear from his last words that he was expecting God to save him from the cross.
Say's who?? Says every dang church I have ever been in. Every one. Every bible camp, every youth group, every bible study...Everything!
He was expecting God to take him, not let it drag on and on.