LUMEN GENTIUM Proclaimed By His Holiness, Pope Paul VI on November 21, 1964
25. Among the more important duties of bishops that of preaching the Gospel has pride of place. For the bishops are heralds of the faith, who draw new disciples to Christ; they are authentic teachers, that is, teachers endowed with the authority of Christ, who preach the faith to the people assigned to them, the faith which is destined to inform their thinking and direct their conduct; and under the light of the Holy Spirit they make that faith shine forth, drawing from the storehouse of revelation new things and old (cf. Mt. 13:52); they make it bear fruit and with watchfulness they ward off whatever errors threaten their flock (cf. 2 Tim. 4-14). Bishops who teach in communion with the Roman Pontiff are to be revered by all as witnesses of divine and Catholic truth; the faithful, for their part, are obliged to submit to their bishops' decision, made in the name of Christ, in matters of faith and morals, and to adhere to it with a ready and respectful allegiance of mind. This loyal submission of the will and intellect must be given, in a special way, to the authentic teaching authority of the Roman Pontiff, even when he does not speak ex cathedra in such wise, indeed, that his supreme teaching authority be acknowledged with respect, and sincere assent be given to decisions made by him, conformably with his manifest mind and intention, which is made known principally either by the character of the documents in question, or by the frequency with which a certain doctrine is proposed, or by the manner in which the doctrine is formulated.
Although the bishops, taken individually, do not enjoy the privilege of infallibility, they do, however, proclaim infallibly the doctrine of Christ on the following conditions: namely, when, even though dispersed throughout the world but preserving for all that amongst themselves and with Peter's successor the bond of communion, in their authoritative teaching concerning matters of faith and morals, they are in agreement that a particular teaching is to be held definitively and absolutely. This is still more clearly the case when, assembled in an ecumenical council, they are, for the universal Church, teachers of and judges in matters of faith and morals, whose decisions must be adhered to with the loyal and obedient assent of faith.
This infallibility, however, with which the divine redeemer wished to endow his Church in defining doctrine pertaining to faith and morals, is co-extensive with the deposit of revelation, which must be religiously guarded and loyally and courageously expounded. The Roman Pontiff, head of the college of bishops, enjoys this infallibility in virtue of his office, when, as supreme pastor and teacher of all the faithful--who confirms his brethren in the faith (cf. Lk. 22:32)--he proclaims in an absolute decision a doctrine pertaining to faith or morals. For that reason his definitions are rightly said to be irreformable by their very nature and not by reason of the assent of the Church, is as much as they were made with the assistance of the Holy Spirit promised to him in the person of blessed Peter himself; and as a consequence they are in no way in need of the approval of others, and do not admit of appeal to any other tribunal. For in such a case the Roman Pontiff does not utter a pronouncement as a private person, but rather does he expound and defend the teaching of the Catholic faith as the supreme teacher of the universal Church, in whom the Church's charism of infallibility is present in a singular way. The infallibility promised to the Church is also present in the body of bishops when, together with Peter's successor, they exercise the supreme teaching office. Now, the assent of the Church can never be lacking to such definitions on account of the same Holy Spirit's influence, through which Christ's whole flock is maintained in the unity of the faith and makes progress in it.
Furthermore, when the Roman Pontiff, or the body of bishops together with him, define a doctrine, they make the definition in conformity with revelation itself, to which all are bound to adhere and to which they are obliged to submit; and this revelation is transmitted integrally either in written form or in oral tradition through the legitimate succession of bishops and above all through the watchful concern of the Roman Pontiff himself- and through the light of the Spirit of truth it is scrupulously preserved in the Church and unerringly explained. The Roman Pontiff and the bishops, by reason of their office and the seriousness of the matter, apply themselves with zeal to the work of inquiring by every suitable means into this revelation and of giving apt expression to its contents; they do not, however, admit any new public revelation as pertaining to the divine deposit of faith.