That charity and brotherly affection are to be religiously and stedfastly practised
In Malachi: “Has not one God created us? Is there not one Father of us all? Why have you certainly deserted every one his brother?” Of this same thing according to John: “Peace I leave with you, my peace I give unto you.” Also in the same place: “This is my commandment, That you love one another, even as I have loved you. Greater love than this has no man, than that one should lay down his life for his friends.” Also in the same place: “Blessed are the peacemakers, for they shall be called the sons of God.” Also in the same place: “Verily I say unto you, That if two of you shall agree on earth concerning everything, whatever you shall ask it shall be given you from my Father which is in heaven.
For wherever two or three are gathered together in my name, I am with them.” Of this same thing in the first Epistle to the Corinthians: “And I indeed, brethren, could not speak unto you as to spiritual, but as to carnal, as to babes in Christ. I have given you milk for drink, not meat: for while you were yet little you were not able to bear it, neither now are you able. For you are still carnal: for where there are in you emulation, and strife, and dissensions, are you not carnal, and walk after man?” Likewise in the same place: “And if I should have all faith, so that I can remove mountains, but have not charity, I am nothing.
And if I should distribute all my goods for food, and if I should deliver up my body to be burned, but have not charity, I avail nothing. Charity is great-souled; charity is kind; charity envies not; charity deals not falsely; is not puffed up; is not irritated; thinks not evil; rejoices not in injustice, but rejoices in the truth. It loves all things, believes all things, hopes all things, bears all things. Charity shall never fail.” Of this same thing to the Galatians: “You shall love your neighbour as yourself.
But if you bite and accuse one another, see that you be not consumed one of another.” Of this same thing in the Epistle of John: “In this appear the children of God and the children of the devil. Whosoever is not righteous is not of God, and he who loves not his brother. For he who hates his brother is a murderer; and you know that no murderer has eternal life abiding in him.” Also in the same place: “If any one shall say that he loves God, and hates his brother, he is a liar: for he who loves not his brother whom he sees, how can he love God whom he sees not?” Of this same thing in the Acts of the Apostles: “But the multitude of them that had believed acted with one soul and mind: nor was there among them any distinction, neither did they esteem as their own anything of the possessions that they had; but all things were common to them.” Of this same thing in the Gospel according to Matthew: If you would offer your gift at the altar, and there rememberest that your brother has ought against you; leave your gift before the altar, and go; first be reconciled to your brother, and then come and offer your gift at the altar. Also in the Epistle of John: “God is love l and he that dwells in love dwells in God, and God in him.” Also in the same place: “He who says he is in the light, and hates his brother, is a liar, and walks in darkness even until now.”
Source: The Treatises of Cyprian (New Advent)