Liberalism is a Sin explains liberalism and how it, on its own terms, constitutes error. Further, it equips the reader to recognize and respond to liberalism present in both himself and his surroundings. Namely, Fr. Salvany grounds the abstraction of liberalism in history and in the (then) present day. In a historical context, he illustrates that ages of heresy may lack clean lines between truth and error. The point highlights the potential for plain error to mask error that masquerades as either truth or harmless opinion. Regarding the present, Fr. Salvany uncovers the hidden manifestations of liberalism baked into everyday life. Practically, his articulation of applied liberalism alerts the reader to the subtleties of liberal thought that, though unseen, saturate his environment. Altogether, the book dissects liberalism and exposes the infrastructure through which it infects modern minds. It is an essential read because it reveals that the infection is often a latent presupposition, which festers undiagnosed in many who do not realize that it is there.