8 The truth of what We have just stated is proven by what has actually takenplace since, of all the sects, deprived as they are of the Catholic Faith anddisagreeing among themselves on religious matters, each one claims that its ownteaching and practices are in accord with Holy Writ. There is no gift of God so sacred, that man cannot abuse it to his own detriment; since, according to the stern warning of Blessed Peter, "the unlearned and unstable wrest" the very Scriptures "to their own destruction" (2 Peter iii., 16). Hence Irenaeus, who lived shortly after the Apostolic age, and who is a faithful interpreter of Apostolic doctrine, always taught that a knowledge of the truth could only be had from the living voice of the Church: "Where the Church is, there is the Spirit of God, and where the spirit of God is found, there is the Church and all grace, and the Spirit is truth" - (Adv. Haer. lib. iii.). "Where, therefore, the gifts of God are placed, it is necessary to learn the truth from those who have in the Church the Apostolic Succession"- (Adv. Haer. lib. iv.). And if Catholics, who may differ on all other matters, are found united in marvellous concord in the faith, there can be no doubt that this is chiefly owing to the authority and power of the "magisterium."
Source: Caritatis Studium (Vatican.va)