That last prepositional phrase, "to the church", is what's in view. Why is this important? Because it is the climactic statement of a whole series of grand and awesome truths about the power and resource that we possess as Christians. It begins in v. 18 where Paul prays that "the eyes of your heart may be enlightened in order that you may know..." Know what? What is so important? From here comes repeated shotgun blasts of descriptors each of which surpasses even our most energized moments of glory in this life. All of that to say that what we tap into in our best hours are mere drops in the oceanic reservoir available to us. What is this resource?
(1) "the hope to which he has called you" which he specifies as "the riches of his glorious inheritance in the saints". God has laid up for us eternal riches for us. What good is that if that's in the future, though? What about now? Well, it is important because this "hope" and "inheritance" both point to one thing: our current status as children of God. Paul links our favored status as children of God with our inheritance in Romans 8:17a which says, "and if children, then heirs—heirs of God and fellow heirs with Christ". This future hope has been secured for us because our fundamental identity has changed. We are forever God's children, therefore, not only do we have a future hope but a present power. This is explicitly stated in the next phrase:
(2) "and his incomparably great power for us who believe": There is no separation between the future hope and the present power. Both come from the same reality of our justified status before God and reconciled relationship that created more than just a "neutral" state for us; we were positively pulled toward the King of Glory and have received crowns of honor as beloved Sons and Daughters, Heirs to the Kingdom. For "believers" only, this power comes. What does this power look like?
(3) "That power is like the working of his mighty strength": Packed into that phrase are 4 words that all mean "power":
(3a) First, there's "power" which is conceptually carried from the first part of v. 19. The term is dunamis which has a very general use. It can specifically refer to a kind of angel, though that's not in view here. It can also refer to a miracle. But in this context it has likely a general reference to "power" in general seeing that the next 3 terms are going to expand and specify a bit on that more general term.
(3b) Second, there's "working" or energeia from which we get "energy" in English. Its 8 NT uses seem to refer mainly if not only to supernatural powers at work. For example, it is the word used to describe God being in control of everything in Philippians 3:21. It refers to resurrection power in Colossians 2:12. The work of Satan is described with this word in 2 Thessalonians 2:9. Such power is available to US as Christians–in us and working for us.
(3c) Third, there's "mighty", iscuos in the Greek. Like dunamis the word has a broad range of uses and functions to emphasize the "capability" of doing something. Its use as an attributive genitive is fitting in this context (hence, "mighty strength", see next).
(3d) Fourth, there's "strength", kratos in the Greek. Its focus is the strength or the intensity of the power to accomplish a deed. It's often interchangeable with dunamis but also is used in the context of sovereign rule. It is used in praises to God in association with his ruling power in Revelation 1:6; 5:13 and Jude 1:25.
Each individual usage is not Paul's point. And there is no indication that he means for us to pause and meditate on each one (though this is not altogether a terrible practice). Rather, it is the rhetorical force generated by the combined uses that packs Paul's polemic punch (just like alliteration!). What is this power and strength for?
Verses 20-22a tell us that God "exerted" these things "in Christ". Ah, this makes good sense to us. Christ is the Son of God, the son of privilege and honor. Naturally, all this power flowed in and through Christ.
Verse 20 tells us that such powers were responsible for Christ's resurrection, the power to conquer death. Needless to say, humanity has not (and never will) conquer death by exercise, pharmaceuticals, or technology. Such is ever beyond our power. Even "immortality" through procreation or the creative spirit (books, paintings, monuments) will one day dissolve to dust. Resurrection power is by its very nature divine power.
If that weren't clear enough, not only is the magnitude of this power measured by conquering death but positively by exaltation to heaven. This is not merely "transport" power, the lifting up of a body to the immaterial, heavenly realm (though the amount of energy it takes for rockets to leave the earth and break orbit is considerable!). But this is the power that comes with authority. As verse 21 clarifies this exaltation put Christ "far above all rule and authority and power and dominion, and above every name that is named, not only in this age but also in the one to come". The power to rule over not only human but likely angelic powers is in view. All of creation will bow to him.
As far as creation itself goes, life and death are among its mightiest powers, hence resurrection power is quite amazing. But considering that all creation itself will submit to Christ, I think, speaks even more of this almightiness. To be certain, this submission is in mind as v. 22a says, "And he put all things under his feet and gave him as head over all things".
Yes, this is Christ who wields all this power and might and glory. And none of this surprises us. He is the exalted Son of Man from Daniel 7. He is the Image of God from Colossians 1. He is the Sustainer of the universe from Hebrews 1. He is God of very God from John 1.
What is a shocker, what rocks us back on our heels is to read the 3 words of what comes in v. 22b:
"to the church"
Why did Christ receive all of this power? To give it "to the church".
What did Christ do wtih all of this power Give it "to the church".
What was the purpose of Christ's life, death, resurrection, and ascension? To give power "to the church".
Where do we find the greatest reserve of power in the world? Where He gave it: "to the church".
And before we shake our heads in abject disbelief or before we are too quick to exalt ourselves as the power-center-of-the-universe, we read at last in v. 23 , "which is his body, the fullness of him who fills all in all". Now here's the connection. Christ has not deposited this power in his church apart from Himself. He has given it to the church because the church is Himself, or more accurately, we are the representation and extension of Himself in the world. We are His body, Christians, "little Christs", types of Christ walking and talking on this fallen orb.
All of this amazing power comes in and through Him. The church is His "body" and thus He is the one who animates it and gives it its life and power. That is why He "fills all in all", perhaps referring to the known creation or perhaps mainly to His body. Thus, no true power of Christ can be exercised apart from His person and purpose. We are not like children who have been handed guns and knives and told to do whatever we want. Instead, we are children who've been handed instruments of power that respond only to proper use, like knives that only can cut if wielded by a surgeon for the saving of lives.
What is this "proper use"? Read the rest of Ephesians to find out! But if you're a Christian you already know. Proper use include things like: growing in holiness, preaching the gospel, serving others, worshiping God, and fighting spiritual warfare. When done by the Spirit and for His purposes, we as Christians wield the mightiest powers in the universe.
If you don't feel that way or don't see your life reflecting this, then now you understand why faith is so important. Faith is not simply something you exercised for that moment of salvation, or for times of struggle. Faith is the conduit by which the Christian exercises this power of God. Only those who start with a belief that this is true will even begin to appropriate it. This is why Satan will attempt ever and always to undermine your faith in this truth. This is why he uses doubt and discouragement and depression as some of his main weapons–because they undercut your access to your only and almighty power. Don't let this happen!
Readers of fantasy novels know the fantasy formula: the story begins with a nobody weakling from a nowhere village. Suddenly, a prophecy is made known and this nobody is foretold to be a mighty king or warrior (or princess for the ladies). Through a series of trials and tribulations, the nobody becomes a somebody and eventually THE Somebody who becomes the most powerful person in the universe (often with the help of a magical sword, ring, stone, necklace, bracelet, wand, etc.).
For the Christian, this is no "fantasy". We all were nobodies before Christ. But because HE endured the trials and tribulations of death and judgment for us and gave all the benefits "to the church", we are who are "in Christ" have become "somebodies", in fact, THE Somebodies of the universe, higher than even the angels! We are the most powerful beings in this universe apart from God Himself. Believe it. Then live it.