18 Bishops, who are the successors of the Apostles, and priests, who according to their proper office cooperate with the Bishops, have been charged with announcing and teaching that gospel which Jesus and His Apostles first announced and taught, and which this Holy See and all the Bishops united to it have preserved and transmitted pure and inviolate through the centuries. The holy pastors, therefore, are not the inventors and the composers of this gospel, but only its authorized custodians and its divinely constituted heralds. Wherefore We Ourselves, and the Bishops together with Us, can and ought to repeat the words of Jesus Christ: "My teaching is not my own, but his who sent me" ( John 7. 16). And to all the Bishops, in every age, can be directed the exhortation of St. Paul: "O Timothy, guard the trust and keep free from profane novelties in speech and the contradictions of so-called knowledge" (I Tim . 6. 20). And so also these words of the same Apostle: "Guard the good trust through the Holy Spirit, who dwells in us" (2 Tim . 1. 14). We are not teachers of a doctrine invented by the human mind. But our conscience obliges us to embrace and follow what Jesus Christ Himself taught, and what He solemnly commanded His Apostles and their successors to teach (Cf. Matt . 28. 19-20).
Source: Ad Sinarum Gentem (Vatican.va)