Rorate Caeli

I am your brother, you are my sister - by unity with him

This authority, however, (though it has been given to man and is exercised by man), is not human but rather divine, granted to Peter by a divine word and reaffirmed to him (Peter) and his successors by the One Whom Peter confessed, the Lord saying to Peter himself, 'Whatsoever you shall bind on earth, shall be bound also in Heaven' etc., [Mt 16:19]. Therefore whoever resists this power thus ordained by God, resists the ordinance of God [Rom 13:2], unless he invent like Manicheus two beginnings, which is false and judged by us heretical, since according to the testimony of Moses, it is not in the beginnings but in the beginning that God created heaven and earth [Gen 1:1]. Furthermore, we declare, we proclaim, we define that it is absolutely necessary for salvation that every human creature be subject to the Roman Pontiff.
Boniface VIII
Unam Sanctam

And so, supported by the clear witness of Holy Scripture, and adhering to the manifest and explicit decrees both of our predecessors the Roman Pontiffs and of general councils, we promulgate anew the definition of the ecumenical Council of Florence, which must be believed by all faithful Christians, namely that the "holy Apostolic See and the Roman Pontiff hold a world-wide primacy, and that the Roman Pontiff is the successor of blessed Peter, the prince of the apostles, true vicar of Christ, head of the whole Church and father and teacher of all Christian people. To him, in blessed Peter, full power has been given by our lord Jesus Christ to tend, rule and govern the universal Church. All this is to be found in the acts of the ecumenical councils and the sacred canons."

Wherefore we teach and declare that, by divine ordinance, the Roman Church possesses a pre-eminence of ordinary power over every other Church, and that this jurisdictional power of the Roman Pontiff is both episcopal and immediate. Both clergy and faithful, of whatever rite and dignity, both singly and collectively, are bound to submit to this power by the duty of hierarchical subordination and true obedience, and this not only in matters concerning faith and morals, but also in those which regard the discipline and government of the Church throughout the world.

In this way, by unity with the Roman Pontiff in communion and in profession of the same faith, the Church of Christ becomes one flock under one Supreme Shepherd.
First Vatican Council
Pastor Aeternus, 3