Pope Clement XIII, A Quo Die (On Unity Among Christians), September 13, 1758: “2. ...But St. Peter confessed that He was the son of the living God, not revealed by flesh and blood but by the Father. (Mt 16.14f.) 3. From this, you can easily see that there is a difference between the sons of light and the sons of the world. The latter disagree among themselves with various and diverse opinions, while the former, initiated into the mysteries of unity, profess the one faith of all by the mouth of one, through the head of all. Therefore, concentrate all your attention on increasing peace among the faithful. Uproars, contentions, rivalries, animosities, and dissensions should be silenced. (2 Cor 12.20.) In this way those who go by the name of Catholic can all be perfect in the same sense, in the same opinion, (1 Cor 1.10.) saying the same thing together, (2 Cor 13.11.) knowing the same thing and understanding it thoroughly. They should understand that if they want to be members of Christ, they cannot have concord with the head if they want to be in disagreement with the members. Nor can those who have not lived in fraternal love be counted as brothers by the Almighty Father.”