103 On this account, in order that no falsification or corruption of the divine law but a true genuine knowledge of it may enlighten the minds of men and guide their conduct, it is necessary that a filial and humble obedience towards the Church should be combined with devotedness to God and the desire of submitting to Him. For Christ Himself made the Church the teacher of truth in those things also which concern the right regulation of moral conduct, even though some knowledge of the same is not beyond human reason. For just as God, in the case of the natural truths of religion and morals, added revelation to the light of reason so that what is right and true, "in the present state also of the human race may be known readily with real certainty without any admixture of error," so for the same purpose he has constituted the Church the guardian and the teacher of the whole of the truth concerning religion and moral conduct; to her therefore should the faithful show obedience and subject their minds and hearts so as to be kept unharmed and free from error and moral corruption, and so that they shall not deprive themselves of that assistance given by God with such liberal bounty, they ought to show this due obedience not only when the Church defines something with solemn judgment, but also, in proper proportion, when by the constitutions and decrees of the Holy See, opinions are prescribed and condemned as dangerous or distorted.
Source: Casti Connubii (Vatican.va)