Behold, how good and pleasant it is for brothers to dwell in unity! It is good and pleasant for brothers to dwell in unity, because when they do so their association creates the assembly of the Church. The term “brothers” describes the bond of affection arising from their singleness of purpose.
We read that when the apostles first preached, the chief instruction they gave lay in this saying: The hearts and minds of all believers were one. So it is fitting for the people of God to be brothers under one Father, to be united under one Spirit, to live in harmony under one roof, to be limbs of one body.