We, the church/ekklesia are His/Jesus’ Body. What God is doing in the world He is doing through us as the fullness of Him that fills all in all
[Ephesians 1:18-23 NASB95] 18 [I pray that] the eyes of your heart may be enlightened, so that you will know what is the hope of His calling, what are the riches of the glory of His inheritance in the saints, 19 and what is the surpassing greatness of His power toward us who believe. [These are] in accordance with the working of the strength of His might 20 which He brought about in Christ, when He raised Him from the dead and seated Him at His right hand in the heavenly [places,] 21 far above all rule and authority and power and dominion, and every name that is named, not only in this age but also in the one to come. 22 And He put all things in subjection under His feet, and gave Him as head over all things to the church, 23 which is His body, the fullness of Him who fills all in all.
[Ephesians 2:4-7 NASB95] 4 But God, being rich in mercy, because of His great love with which He loved us, 5 even when we were dead in our transgressions, made us alive together with Christ (by grace you have been saved), 6 and raised us up with Him, and seated us with Him in the heavenly [places] in Christ Jesus, 7 so that in the ages to come He might show the surpassing riches of His grace in kindness toward us in Christ Jesus.
[Colossians 1:24-28 NASB95] 24 Now I rejoice in my sufferings for your sake, and in my flesh I do my share on behalf of His body, which is the church, in filling up what is lacking in Christ’s afflictions. 25 Of [this church] I was made a minister according to the stewardship from God bestowed on me for your benefit, so that I might fully carry out the [preaching of] the word of God, 26 [that is,] the mystery which has been hidden from the [past] ages and generations, but has now been manifested to His saints, 27 to whom God willed to make known what is the riches of the glory of this mystery among the Gentiles, which is Christ in you, the hope of glory. 28 We proclaim Him, admonishing every man and teaching every man with all wisdom, so that we may present every man complete in Christ.
We have been called, in fact saved, with a purpose beyond salvation alone. Saved not just from judgement, but unto an eternal purpose. We are to manifest the fullness of Christ, and the fullness of God’s love in Jesus; what Paul calls “filling up what is lacking in Christ afflictions” here in Colossians 1:24. Understand Jesus left nothing unfinished or unfulfilled in His own suffering and conquering of death and the grave. We are not making Him complete or His atoning work more complete. We are simply filling out the message He brought and manifested in His flesh from the Father. Making the good news and revelation of the mystery known and evident. Sometimes by our own suffering and sacrifice. As it required much from Him in love, service, sacrifice, obedience, the laying down of His life for others in obedience to the Father’s will and purpose, so it often requires much from us. As Jesus manifested the fullness of the Father’s love and glorified Him, so are we to, do we now, manifest in Christ that same full love and glorify the Father and the Son.
[John 17:3-11 NASB95] 3 “This is eternal life, that they may know You, the only true God, and Jesus Christ whom You have sent. 4 “I glorified You on the earth, having accomplished the work which You have given Me to do. 5 “Now, Father, glorify Me together with Yourself, with the glory which I had with You before the world was. 6 “I have manifested Your name to the men whom You gave Me out of the world; they were Yours and You gave them to Me, and they have kept Your word. 7 “Now they have come to know that everything You have given Me is from You; 8 for the words which You gave Me I have given to them; and they received [them] and truly understood that I came forth from You, and they believed that You sent Me. 9 “I ask on their behalf; I do not ask on behalf of the world, but of those whom You have given Me; for they are Yours; 10 and all things that are Mine are Yours, and Yours are Mine; and I have been glorified in them. 11 “I am no longer in the world; and [yet] they themselves are in the world, and I come to You. Holy Father, keep them in Your name, [the name] which You have given Me, that they may be one even as We [are.]
The heart of Jesus and the eternal purpose of God revealed in this prayer also reveals much regarding His disciples in the world to glorify Him/Jesus, and our being in Him as one even as He and the Father are one.
We, the church, as His body, the fullness of Jesus, and as His disciples, have a message, mission, and purpose in the world. Even as Paul felt charged with revealing a mystery hidden for ages, so now are we to reveal the mystery of Christ in us…. the hope of Glory. Jesus’ prayer, as He continues, makes it clearly evident that we are (sent) in the world even as He was, and even as He manifested the glory of the Father and being one with Him, so, we too, are to manifest Him and His glory. We are in the world, but we are not of it, as we are also seated with Him, in Him, in heavenly places.
[John 17:15-24 NASB95] ... 15 “I do not ask You to take them out of the world, but to keep them from the evil [one.] 16 “They are not of the world, even as I am not of the world. 17 “Sanctify them in the truth; Your word is truth. 18 “As You sent Me into the world, I also have sent them into the world. 19 “For their sakes I sanctify Myself, that they themselves also may be sanctified in truth. 20 “I do not ask on behalf of these alone, but for those also who believe in Me through their word; 21 that they may all be one; even as You, Father, [are] in Me and I in You, that they also may be in Us, so that the world may believe that You sent Me. 22 “The glory which You have given Me I have given to them, that they may be one, just as We are one; 23 I in them and You in Me, that they may be perfected in unity, so that the world may know that You sent Me, and loved them, even as You have loved Me. 24 “Father, I desire that they also, whom You have given Me, be with Me where I am, so that they may see My glory which You have given Me, for You loved Me before the foundation of the world.
John obviously, in being with Jesus and in the garden where He prayed, caught much in the Spirit. Even if he did not comprehend the importance of it in the moment. In His epistle He would speak of who we are, and “He that is in us”. And, He would emphasize our need to testify of Jesus coming in the flesh as the only begotten, something He personally witnessed. And he would; speak of the power of our testimony of Him, manifesting Him, in our love for one another. That love is the primary way we will manifest His fullness. Without great commentary let me offer this from 1 John 4.
[1John 4:2-16 NASB95] 2 By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God; 3 and every spirit that does not confess Jesus is not from God; this is the [spirit] of the antichrist, of which you have heard that it is coming, and now it is already in the world. 4 You are from God, little children, and have overcome them; because greater is He who is in you than he who is in the world. 5 They are from the world; therefore they speak [as] from the world, and the world listens to them. 6 We are from God; he who knows God listens to us; he who is not from God does not listen to us. By this we know the spirit of truth and the spirit of error. 7 Beloved, let us love one another, for love is from God; and everyone who loves is born of God and knows God. 8 The one who does not love does not know God, for God is love. 9 By this the love of God was manifested in us, that God has sent His only begotten Son into the world so that we might live through Him. 10 In this is love, not that we loved God, but that He loved us and sent His Son [to be] the propitiation for our sins. 11 Beloved, if God so loved us, we also ought to love one another. 12 No one has seen God at any time; if we love one another, God abides in us, and His love is perfected in us. 13 By this we know that we abide in Him and He in us, because He has given us of His Spirit. 14 We have seen and testify that the Father has sent the Son [to be] the Savior of the world. 15 Whoever confesses that Jesus is the Son of God, God abides in him, and he in God. 16 We have come to know and have believed the love which God has for us. God is love, and the one who abides in love abides in God, and God abides in him.