In Eph. 1:10 Paul discloses God’s grand, comprehensive and ultimate purpose – far greater than our own personal salvation – that … He might gather together in one all things in Christ, both which are in heaven and which are on earth. Here you have the bottom line of God’s heart, the central purpose of His decrees of grace, that for which He and all creation have groaned and travailed for – the re-unification of all things.
In the manifold wisdom of God, He created a variety of beings. In His goodness and love, He called out of that variety, some from every sort, to reconcile to Himself and to each other. God united a variety of persons under one head, Jesus Christ; who, in His person, is the sum of all of their natures and conditions (taking the form of a bondservant, and coming in the likeness of men – Phil 2:7), and yet He is distinct from them (yet without sin – Heb 4:15).
The unification of which Paul writes in this verse includes that which are both in heaven and which are on earth. So the great divide that exists between God and man is bridged, but then, there also is reconciliation between man and man. The barriers that separate human beings from one another are torn down in Christ. He … has broken down the middle wall of separation, having abolished in His flesh the enmity, … so as to create in Himself one new man from the two, thus making peace, and that He might reconcile them both to God in one body through the cross … (see Eph 2:14-17). To see what this ultimate unity looks like, read Revelation chapters 4-5. God is glorified as a diverse people, who we are told, are from every tribe and tongue and nation, worship and enjoy Him together forever (Rev 5:9