XII. In case of difference of opinion between the Vicar and the bishops, the bishop of Rome must be consulted. The subordination of authorities in the Church expounded.
But if in that which you believed necessary to be discussed and settled with the brethren, their opinion differs from your own wishes, let all be referred to us, with the minutes of your proceedings attested, that all ambiguities may be removed, and what is pleasing to God decided. For to this end we direct all our desires and pains, that what conduces to our harmonious unity and to the protection of discipline may be marred by no dissension and neglected by no slothfulness. Therefore, dearly beloved brother, you and those our brethren who are offended at your extravagant conduct (though the matter of complaint is not the same with all), we exhort and warn not to disturb by any wrangling what has been rightfully ordained and wisely settled.
Let none “seek what is his own, but what is another's,” as the Apostle says: “Let each one of you please his neighbour for his good unto edifying.” For the cementing of our unity cannot be firm unless we be bound by the bond of love into an inseparable solidity: because “as in one body we have many members, but all the members have not the same office; so we being many are one body in Christ, and all of us members one of another.” The connection of the whole body makes all alike healthy, all alike beautiful: and this connection requires the unanimity indeed of the whole body, but it especially demands harmony among the priests.
And though they have a common dignity, yet they have not uniform rank; inasmuch as even among the blessed Apostles, notwithstanding the similarity of their honourable estate, there was a certain distinction of power, and while the election of them all was equal, yet it was given to one to take the lead of the rest. From which model has arisen a distinction between bishops also, and by an important ordinance it has been provided that every one should not claim everything for himself: but that there should be in each province one whose opinion should have the priority among the brethren: and again that certain whose appointment is in the greater cities should undertake a fuller responsibility, through whom the care of the universal Church should converge towards Peter's one seat, and nothing anywhere should be separated from its Head.
Let not him then who knows he has been set over certain others take it ill that some one has been set over him, but let him himself render the obedience which he demands of them: and as he does not wish to bear a heavy load of baggage, so let him not dare to place on another's shoulders a weight that is insupportable. For we are disciples of the humble and gentle Master who says: “Learn of Me, for I am gentle and humble of heart, and you shall find rest for your souls. For My yoke is easy and My burden light.” And how shall we experience this, unless this too comes to our remembrance which the same Lord says: “He that is greater among you, shall be your servant. But he that exalts himself, shall be humbled: and he that humbles himself, shall be exalted.”
Source: Letters (New Advent)