The Apostle Paul writes his first letter to the Corinthians in order to preach and expose the Christian doctrine to that church. In a passage of the letter he warns about fornication and affirms:"But whoever is united with the Lord is one with him in spirit" 1 Corinthians 6:17.
This text has a similarity with the following "That all of them may be one, Father, just as you are in me and I am in you" John 17:21. Being one spirit with God, that is the essence of the communion and the concord, is the union of minds and hearts. From there the idea of one heart, one mind, one will, the will of the Providence.
Talk about of the Concord is talk about  Providence and the Divine Plan. When we are one spirit with God we are not affected by the passions and we act sensibly. The hatred, the contempt, the fear, affect human reason and lead us into error.
The Concord is reflected in the concept of "not act by passion" and "minimize the suffering", when we are one with God we heal our feelings and thoughts about others, we heal ourselves and "see his Kingdom" John 3: 3, reaching the contemplative activity and the Gift of Eternal Life, or to say the blessings that God gives to us in this life in advancement of the life life or the life in glory.
The path to the Union with God is the retitude, "Do for others what you would like to do for you" and the Spiritual Gift of Serenity, the Constancy, the Firmness, the Devotion. Through the Constancy we bear fruits,  "The beginning of wisdom is the fear of the Lord" Proverbs 1: 7. The Agape, the spiritual love, the love of God is the result of living these important gifts, with them we become true sons of God and brothers of the neighbor.