24 In defining the limits of the obedience owed to the pastors of souls, but most of all to the authority of the Roman Pontiff, it must not be supposed that it is only to be yielded in relation to dogmas of which the obstinate denial cannot be disjoined from the crime of heresy. Nay, further, it is not enough sincerely and firmly to assent to doctrines which, though not defined by any solemn pronouncement of the Church, are by her proposed to belief, as divinely revealed, in her common and universal teaching, and which the Vatican Council declared are to be believed "with Catholic and divine faith."(27) But this likewise must be reckoned amongst the duties of Christians, that they allow themselves to be ruled and directed by the authority and leadership of bishops, and, above all, of the apostolic see. And how fitting it is that this should be so any one can easily perceive. For the things contained in the divine oracles have reference to God in part, and in part to man, and to whatever is necessary for the attainment of his eternal salvation. Now, both these, that is to say, what we are bound to believe and what we are obliged to do, are laid down, as we have stated, by the Church using her divine right, and in the Church by the supreme Pontiff. Wherefore it belongs to the Pope to judge authoritatively what things the sacred oracles contain, as well as what doctrines are in harmony, and what in disagreement, with them; and also, for the same reason, to show forth what things are to be accepted as right, and what to be rejected as worthless; what it is necessary to do and what to avoid doing, in order to attain eternal salvation. For, otherwise, there would be no sure interpreter of the commands of God, nor would there be any safe guide showing man the way he should live.
Source: Sapientiae Christianae (Vatican.va)