Your statement contradicts the scripture. I believe you are misunderstanding verse 1. The letter is written TO the church leaders, but it is not only ABOUT them.
In verse 9 Paul says that God has made known to them the mystery of his will. And what is the mystery of his will. That is answered in verse 10. Paul wrote that Jesus is to unite ALL THINGS in him, including things in Heaven. Paul didn't write to unite "all Christians" or "all believers". No, he wrote "ALL THINGS".
Paul, an apostle of Christ Jesus by the will of God,
Ephesians 1:1-10
To the saints who are in Ephesus, and are faithful[a] in Christ Jesus:
2 Grace to you and peace from God our Father and the Lord Jesus Christ.
3 Blessed be the God and Father of our Lord Jesus Christ, who has blessed us in Christ with every spiritual blessing in the heavenly places, 4 even as he chose us in him before the foundation of the world, that we should be holy and blameless before him. In love 5 he predestined us for adoption to himself as sons through Jesus Christ, according to the purpose of his will, 6 to the praise of his glorious grace, with which he has blessed us in the Beloved. 7 In Him we have redemption through His blood, the forgiveness of our trespasses, according to the riches of His grace, 8 which He lavished upon us, in all wisdom and insight 9 making known[c] to us the mystery of? His will, according to His purpose, which he set forth in Christ[d] 10 as a plan for the fullness of time, to unite all things in Christ, things in heaven and things on earth in Him.