Throughout Ephesians, Paul is concerned to unfold God’s plan to “unite all things” in Christ (Eph. 1:10), a design to bring together people from every tribe and tongue in submission to the Lord Jesus. Until this plan is consummated at the return of Christ, this unity will not be a full reality, for the Father will allow at least a portion of mankind to rebel against Him. At Jesus’ second advent, there will be a final separation of humanity into two groups — one people unified in worship and adoration of the one true Creator God and another group that is cast into the outer darkness, where they will experience disharmony among themselves and the wrath of the Creator forever (Matt. 8:5–13).
In the era between the ascension and return of Christ, the church is the beachhead in the Lord’s plan to fashion this one people. It manifests in part the unity to come on that final day, for as believing Jews and Gentiles live together in love, creation catches a glimpse of the future. Jesus has done what is necessary to form this unified church (Eph. 2:11–22), and Christians have the important duty of maintaining this oneness, a unity rooted and grounded in the abundant love of our Savior (3:14–4:3). That we might thoroughly understand the importance of unity, the apostle moves on in today’s passage to more fully emphasize the oneness of the body of Christ. Beginning in Ephesians 4:4, Paul employs a sevenfold repetition of the term one, looking at each of the aspects that knit the church together.
Verse 4 speaks of one body, one Spirit, and one hope. Spirit, of course, is the Holy Spirit, the one who joins believers to Jesus and to one another, making believers from different backgrounds able to live together as they strive, with His help, to maintain this unity. The one body is the unified community of believers, which includes both those living today and those already enjoying the unmediated presence of Christ in glory (Heb. 12:18–24). Our one hope is the objective reality of resurrected life that we will experience in fullness in the new heaven and earth. Even now, the Holy Spirit grants to all of God’s elect the assurance of this hope, a hope that belongs to everyone who trusts in Christ alone for salvation (Rom. 8:18–30).