Psalm 133:1 (ESV) … “Behold, how good and pleasant it is when brothers dwell in unity!”
It is a sight worth seeing. It is what God covets for His people. It is what Satan dreads and what he works night and day to undo. It is that for which Jesus Himself prayed beneath the lengthening shadow of the cross. It is the one thing, God says, that will convince people that the church has something the world does not have. It is what the Holy Ghost came to achieve in His baptizing work. It is what the Jews saw so convincingly displayed in the infant Jerusalem church—a church where one and all, rich and poor, bond and free, great and small, young and old, gifted and retarded, had all things in common. The unity God wants for His people is not deadly uniformity, not an imitation ecumenism; it is not a unity brought about by doctrinal compromise, political expediency, or organizational efficiency. (The church is not an organization but an organism; it’s symbol for this age is a body, not a business.) The unity of the Spirit is not a unity brought about by some extrabiblical experience indulged at the expense of sound doctrine; the early church continued steadfastly in the apostles’ doctrine, as well as in fellowship.
How rare and exotic a plant it is on earth. “How good and how pleasant it is for brethren to dwell together in unity.” Shadows of Cain and Abel at once start to life. Man’s first sin separated man from God; his second sin separated man from man. Abel’s blood, seeping into the soil, crying aloud to heaven for vengeance, put an end to the brotherhood of man.
Nobody can organize brotherhood. People can join lodges and clubs, they can found United Nations organizations and promote ecumenical movements all in vain. There can be no universal brotherhood of man apart from a universal fatherhood of God, and the Bible makes clear that God is not the father of all. He is the creator of all, but He is the father only of those who are born again, born from above, born of the Spirit of God. What the world is looking for is a practical demonstration of brotherhood and unity among the children of God.
 Phillips, J. (2012). Exploring Psalms 89–150: An Expository Commentary (Vol. 2, Ps 133:1). Kregel Publications; WORDsearch Corp.