Mere Christianity, in The Complete C. S. Lewis Signature Classics

p. 37

Lewis states the Christian doctrine of Christ’s atonement as this: “Christ’s death has somehow put us right with God and has given us a fresh start.  Theories as to how it did this are another matter.”  But you don’t need to believe this theory or that one for the atonement to give you a fresh start.  Christians disagree about the theories.  They are not necessary to our faith any more than understanding exactly how a meal (with its vitamins and proteins, etc.) nourishes us is necessary for it to nourish us.  People were nourished and pleased by the nourishment long before anybody understood about vitamins and proteins.