God has a mystery — and He makes it known to us, says Paul, because He is pleased to do so. God’s mystery is that He intends “to bring all things in heaven and on earth together under one head, even Christ.”
How mysterious it is that God — long before He created time — knew and chose me and you in love. (How humbling!) How mysterious it is that God — long before Abram was born — selected him to be the father of all who are born-again of water and Spirit. How mysterious it is that God — who knows all that is and all that will be — is nevertheless not the author of evil, but only of good. How mysterious it is that God eventually will unite and place everything (not some things) underneath the head, who is His Son, Jesus the Christ. Does this mean that at some future point — perhaps when time has ended and there is only eternity — all will be perfect again? Will everything be able then to say, ‘Oh Death, where is your sting?’ because death and hell will be no more?
Is it possible that at some point our adversary will actually cease to exist, or that he himself will be brought under the head of Christ? Not only brought under His Head, but united with everything else? The Word here in Paul’s letter to the Ephesian church is hard to fathom.
A mystery understood is no longer mysterious. Paul says that God reveals this mystery — that He tells us all will be united under Christ. But, how this is to be remains a mystery. With man, much is impossible. With God, all things are possible.
Grace Partakers 
Is Ephesians 1 talking about things that have yet to happen or things that have already happened?
Eric,
Depends upon what part of Ephesians 1. But, I’d say both, assuming you are asking about the whole chapter. God chose us before we were born, and at some future point He will unite everything in Christ — this is His ultimate purpose.
Love in our Lord, Carley