Our 10th point of 11 doctrinal statements reads: "The real spiritual unity in Christ of all redeemed by His precious blood." This is actually an improvement upon the Apostle's Creed, which has the phrase, "and I believe in the holy catholic church," which can be confused for the works-gospel denomination known as the Roman Catholic church. "Catholic", in its truest sense, simply means "universal throughout all time".
Because of Christ's finished work of atonement on the cross, He has redeemed (bought back) all His people, united them together in Christ, and adopted all those circumcised in heart, of whom the whole family in heaven and earth is named. Paul under inspiration speaks often of this union with Christ, observing we are buried with Him by baptism into death; planted together in the likeness of His death; our old man is crucified with Him; and encouraging us that we shall also live with Him.
This unity of all true believers is a very real phenomenon. One time, some aunts of my wife's mother visited from Lebanon, and we sung hymns after dinner. They didn't know English, and I wasn't about to attempt Arabic, yet we knew both the same tune. I could tell we were one in Christ by how they sang. Babel's barrier had been broken. We know we're in the midst of family when we share the same Father and Savior.
Like all spiritual gifts, they must be kindled. We are to endeavour to keep the unity of the Spirit in the bond of peace. There is one body, and one Spirit, even as ye are called in one hope of your calling. For as the body is one, and hath many members, and all the members of that one body, being many, are one body: so also is Christ. This doctrine is so important, that the Lord Jesus prayed that they all may be one; as thou, Father, art in me, and I in thee, that they also may be one in us: and that they may be made perfect in one; and that the world may know that thou hast sent me, and hast loved them, as thou hast loved me.
Abraham's promise of a great seed will be fulfilled when in heaven we behold a great multitude, which no man could number, of all nations, and kindreds, and people, and tongues, stood before the throne, and before the Lamb, clothed with white robes. What a glorious sight!