9 It is clear that We are discussing a serious matter, with which our eternal salvation is very intimately connected. Some men, as the Apostle of the Gentiles warns us, are "ever learning yet never attaining knowledge of the truth." (5) They contend that the human mind can discover no truth that is certain or sure; they reject the truths revealed by God and necessary for our eternal salvation.
Source: Ad Petri Cathedram (Vatican.va)