In Eph. 1:9,10 Paul makes a statement regarding the mystery which has baffled many students of the Word:
“Having made known unto us the mystery of His will, according to His good pleasure which He hath purposed in Himself:
“That in the dispensation of the fulness of times He might gather together in one all things in Christ, both which are in heaven, and which are on earth; even in Him.”
This will be the glorious consummation of the mystery but we, of the dispensation of grace, are to show men and angels that true oneness is to be found only in Christ (Eph. 3:9-11).
The world knows nothing of this perfect oneness and, indeed, the Church does not experience it — except in Christ. There is no true oneness anywhere — in the world or in the Church — except in Christ. We might illustrate this by two members of the body: our two arms. They hang from opposite sides of the body yet work together as one. But wherein lies their oneness? The answer is: In the head. It is the head which makes my arms and hands operate as one, and so our oneness as members of Christ’s Body, is in Christ, the Head. It is the recognition of Christ as our Head, then, and this alone, that can make us one, experien- tially. Thus the Apostle says:
“Let this mind be in you, which was also in Christ Jesus” (Phil. 2:5).
Soon enough the Lord will take us out of this world and all those events will transpire which will finally bring in “the fulness of [the] times,” when all in heaven and earth will be “gathered together in one… in Christ”! “What a day of rejoicing that will be”! source