Augustine of Hippo

"In this are manifested the children of God and the children of the devil. Whosoever is not righteous is not of God, neither he that loveth not his brother." Aye, now indeed it is manifest of what he speaks: "Neither he that loveth not his brother." Therefore, love alone puts the difference between the children of God and the children of the devil. Let them all sign themselves with the sign of the cross of Christ; let them all respond, Amen; let all sing Alleluia; let all be baptized, let all come to church, let all build the walls of churches: there is no discerning of the children of God from the children of the devil, but only by charity. They that have charity are born of God: they that have it not, are not born of God. A mighty token, a mighty distinction! Have what thou wilt; if this alone thou have not, it profiteth thee nothing: other things if thou have not, have this, and thou hast fulfilled the law. "For he that loveth another hath fulfilled the law," saith the apostle: and, "Charity is the fulfilling of the law." I take this to be the pearl which the merchant man in the Gospel is described to have been seeking, who "found one pearl, and sold all that he had, and bought it." This is the pearl of price, Charity, without which whatever thou mayest have, profiteth thee nothing: which if alone thou have, it sufficeth thee.