Second Vatican Council, Declaration "Dignitatis Humanae" 14

In the formation of their consciences, the Christian faithful ought carefully to attend to the sacred and certain doctrine of the Church. For the Church is, by the will of Christ, the teacher of the truth. It is her duty to give utterance to, and authoritatively to teach, that truth which is Christ Himself, and also to declare and confirm by her authority those principles of the moral order which have their origins in human nature itself.