The Catechism of the Summa - Tertia Pars - XLII. OF THE SACRAMENT OF HOLY ORDERS; OF PRIESTS, BISHOPS, AND THE SOVEREIGN PONTIFF; AND OF THE CHURCH, MOTHER OF SOULS (D)

(D)
Has the Bishop of Rome or the Sovereign Pontiff powers which other bishops have not?

As regards the administration of the sacraments his powers are the same as those of other bishops. But as regards the power of jurisdiction, which refers to the government of the Church, and to the administration of the sacraments to such and such particular individuals, his power is absolute and extends to the Church in the entire universe; whereas the power of jurisdiction of other bishops extends only to a part of the universal Church, viz., to their own diocese; but even as regards their own diocese, their power derives its nature and its exercise from the power of the Sovereign Pontiff (XL. 6).

Why does this supreme power in the order of jurisdiction belong to the Sovereign Pontiff?

Because the perfect unity of the Church demands that this supreme power should belong to him alone. For this reason Jesus Christ charged Simon Peter to feed His flock; and the Roman Pontiff is the one and only legitimate successor of St. Peter unto the end of time (XL. 6).

It is then from the Sovereign Pontiff that depends every man's union with Jesus Christ through the sacraments, and consequently his supernatural life and eternal salvation?

Yes; for although it is true that the grace of Jesus Christ is not in an absolute way dependent upon the reception of the sacraments themselves when it is impossible to receive them, at least in the case of adults -- and that the action of the Holy Ghost can supplement this defect provided the person is not in bad faith; it is, on the other hand, absolutely certain that no one who separates himself knowingly from communion with the Sovereign Pontiff can participate in the grace of Jesus Christ, and that in consequence if he dies in that state he is irremediably lost.

Is it then in this sense that it is said no one can be saved outside the Church?

Yes, for no one can hold God as his Father who does hold the Church for his Mother.

Next - The Catechism of the Summa - Tertia Pars - XLIII. OF THE SACRAMENT OF MATRIMONY; OF ITS NATURE, IMPEDIMENTS, DUTIES; OF DIVORCE; OF SUBSEQUENT MARRIAGE; AND OF ESPOUSALS (A)