Anger, Envy, Lust, Pride, Gluttony, Sloth and Covetousness are the seven capital or deadly sins. They -- along with vainglory, ambition, avarice, and an over-reliance on one's own intellect to the detriment of growth in faith -- are among the hidden enemies of the priesthood. Ignorance of them and the subtle ways in which they can eat away at the moral fiber of priests can prove disastrous for the individuals and for the Church they have vowed to serve. St. Thomas Aquinas along with Scripture, the Catechism of the Catholic Church and the Code of Canon Law provide invaluable insights into how to recognize and confront these vices when they raise their ugly heads. This study is meant to help priests and seminarians reckon with them in a healthy and faith-filled way so that they will not be taken aback by the trials these hidden enemies bring about.