In Paul's list of blessings accomplished by Jesus Christ, he gives us a wonderful BIG PICTURE glimpse at God's eternal purpose. In addition to redeeming us with his blood, resulting in the forgiveness of our trespasses (verse 7), in Christ we have been giving revelation; that is, knowledge of the mystery of God's plan ("making known to us the mystery of his will," v9a). Then Paul begins to unlock for us this great 'mystery' (in Scripture, a mystery is something we would not naturally know unless God reveals it to us):
...according to his purpose, which he set forth in Christ as a plan for the fullness of time, to unite all things in him, things in heaven and things on earth. Ephesians 1:9b-10, ESVThis is grand, epic language indeed! God's will, according to his purpose, which he will bring about in the 'fullness of time,' is to UNITE all things in Jesus, whether these things be in heaven or in earth. What is this talking about?
Peter O'Brien is very helpful on this point (drawing from C.C. Caragounis, Mysterion). This ReUnification means that all will bow to Christ. Christ will have the preeminence in all things, ruling in every realm. The word unite (Greek anakephalaioō) means to ‘sum up all things’ (its only other occurrence in the NT is Romans 13:9, where all the commandments are summed up in the command to love your neighbor – Stott). “Christ is the sphere in which God sums up the cosmos… God’s saving purposes, planned from eternity, had as their final goal the uniting of all things in heaven and earth in Christ.. (God is) bringing together the fragmented, alienated elements of the universe in Christ as the focal point” (O’Brien).
We cannot overstate the importance of Jesus Christ!
God purposed for Christ to rule over all and be the center of all – things in heaven (represented by the 'powers' so frequentlymentioned in Ephesians) and things on earth (represented by the church, made up of Jews and Gentiles). The obstacles to this grand purpose were the rebellion of the powers in the heavenlies, and the alienation of men from God and each other on earth (Caragounis, quoted in O’Brien).