The one Body of Christ is the one fullness as the unique expression of the unique One who fills all in all (Eph. 1:23), leaving no ground for anyone to make any kind of division under any kind of excuse (Rom. 16:17).
The one Body of Christ is also the organism of the processed and consummated Triune God (Eph. 3:17-19), constituted with all the members of Christ (Rom. 12:5; 1 Cor. 10:17).
The one Body of Christ is the one new man (Eph. 2:15; Col. 3:10-11). There is no possibility of division within the one new man. Actually, within the one Body you cannot make any division. To make the churches autonomous is like making the members of your body into different autonomies. Could any part of Christ's Body be autonomous? Even the fifty states of the United States are not altogether autonomous. There is still one federal government, one constitution, one diplomacy, one currency, one defense, one postal system, and one highway system. How foolish it would be to make the states autonomous in any of these matters. The concept of autonomy is awful because it makes the churches separate and some even divided from one another. We should not forget that all the believers are the one new man, and this one new man includes all the local churches.
Christ is all the members of the one new man. Christ is you, and Christ is me. Christ is every member of the one new man. Because of this Paul asked, "Is Christ divided?" (1 Cor. 1:13). Since Christ cannot be divided, how could the Body of Christ as the one new man be divided?
Christ not only is all the members of the one new man, but also is in all the members of the one new man for the accomplishment of God's eternal economy (Eph. 3:8-10). The Body is for Christ's satisfaction, and the one new man is for the accomplishment of God's eternal economy. This could never be consummated in the way of divisions.
The one Body is the one church of God (Eph. 1:22; 1 Cor. 10:32b), manifested in many localities (Rev. 1:11) as many local churches (v. 4).