First published in 1931, in Sin and the New Psychology the author has confronted, not with denunciation but with reasoned argument, the common view that there is no such thing as sin in the Christian sense, because "complexes" now are all. So far from an internecine conflict obtaining between Christian teaching about sin and the New Psychology (taken as equivalent to psychoanalysis), he urges that in a real degree they are pursuing the same end. The method of psychotherapy, as he contends, is in principle identical with that which Christianity employs for the cure and eradication of sin.

The book discusses important themes like sketch of the new psychology; the Christian doctrine of sin; psychic evil and the essence of sin; original sin and the unity of the race; temptation and the unconscious impulse; the sense of guilt and the inferiority complex; confession and repression; forgiveness and transference; and sanctification and sublimation. This book is an important historical reference work for scholars of psychoanalysis, Christian theology, psychology and religion in general.