6 The Apostles, following in the steps of the divine Master, and conforming to His word and commands, were unceasing in their exhortation to the faithful: "Before all things have a constant mutual charity among yourselves". "But above all these things have charity which is the bond of perfection". "Dearly beloved, let us love one another for charity is God". Our brethren of the first Christian ages faithfully observed these commands of Jesus Christ and the Apostles. They belonged to different and rival nations; yet they willingly forgot their causes of quarrel and lived in perfect concord, and such a union of hearts was in striking contrast with the deadly enmities by which human society was then consumed.
Source: Pacem, Dei Munus Pulcherrimum (Vatican.va)