19 As Vicar of Him Who in a decisive hour pronounced before the highest earthly authority of that day, the great words: "For this was I born, and for this came I into the world; that I should give testimony to the truth. Every one that is of the truth, hearest My voice" ( Saint John xviii. 37), We feel We owe no greater debt to Our office and to Our time than to testify to the truth with Apostolic firmness: "to give testimony to the truth." This duty necessarily entails the exposition and confutation of errors and human faults; for these must be made known before it is possible to tend and to heal them. "You shall know the truth and the truth shall make you free" ( Saint John viii. 32).
Source: Summi Pontificatus (Vatican.va)