Definition and meaning of the concord in the bible
The Concord: "We are all one". The concord is by definition a form of friendship, is ethical friendship. Jesus teach to us about the concord:"That all of them may be one Father, just as you are in me and I am in you", John 17:21; there is in the new testament another teaching about the concord: "All the believers were one in heart and mind. No one claimed that any of their posessions was their own, but they shared everything they had", Acts 4:32.
There are many forms of friendship, but that true and most excellent is one where our neighbor, the other matters. When we act according to the golden rule our neighbor matters, and this rule of universal love is perfected in the love for the good, the spiritual love, the Agape, giving rise to another excellence the Concord, and that is the union of hearts.
Recall that the Parable of the Good Samaritan (Luke 10: 25-37), teaches that men sin or act by ethical principles. The opposite of the Golden Rule, the the law of God, is the sin. When men practice the sin, the friendship between them can only stay long as there are common goals and momentary happiness of fun. The Good Samaritan is a friend of his neighbor, as God who acts through Providence (spiritual gift of Providence).
Friendship based simply on the sympathy and empathy lacking is a frivolous and superficial friendship.
Friendship among men born from the desire for happiness and it is from here that Justice relates to the friendship. But justice does not perfect the friendship, simply maintaining compliance.
Friendship between men is not enough, we need the friendship with God, the perfect friendship. or to say our relationship with the creation.
The Justice gives birth to the general friendship (Aristotle), but the Golden Rule gives birth to the universal friendship, the ethic friendship. Justice establishes the friendship between those who are like us, and this is the general friendship. But the Golden Rule establishes a friendship with those whose state of helplessness "can not repay" our effort, that is why the Golden Rule is universal friendship, the Golden Rule expands our friendship from who are such us (justice) to our neighbors, and like the Good Samaritan we became friends of God and Blessed.
The Golden Rule is in direct relation to the Spiritual Gift of Mercy, in relation to the ethical and the divine.
The true friendship, the friendship with God, the most durable, is one that feeds on our excellences and perfections or to say our spiritual gifts (qualities of God), of our Mercy and ultimately is one that is attached to the Concord, the friendship with God and the neighbor , to the union of minds and hearts. The Concord is the perfection of friendship, the sympathetic and empathetic friendship, under it "we are all one."
This is the nature of those who are truly brothers, those who are truly "sons of God".