The following is an excerpt from Dan Cruver’s Reclaiming Adoption. This is important in showing the goal of redemption being adoption. The two cannot be separated!
Paul is the only writer in Scripture to employ the term adoption, and he does so in four separate passages. Looking at each passage in turn transports us to four crucial events in the grand story of redemption. Together, these events reveal the adoption of sinners to be God’s ultimate purpose. They also have the power to completely overhaul our understanding of adoption.
1. Before Time (Ephesians 1:4-5)
In this passage, Paul states that God the Father “chose us in him before the foundation of the world, that we should be holy and blameless before him. In love he predestined us for adoption as sons through Jesus Christ.” Thus, we see that God’s first work of adoption happened even before he created the universe. God did this, Paul emphasizes, “in love.” Before the first molecule was formed, God marked us out with incomparable care—he predestined us—for the great privilege of being his beloved children through adoption. Adoption was not a divine afterthought. It was in God’s triune mind and heart before the first tick of human history’s clock. Adoption therefore predates the universe itself. Only God and his triune love are “bigger” than adoption.
2. Israel (Romans 9:4)
Here, Paul identifies adoption as one of the great privileges Israel enjoyed as God’s chosen people: “They are Israelites, and to them belong the adoption, the glory, the covenants, the giving of the law, the worship, and the promises.” Scholars believe that Israel received adoption—that is, officially became God’s corporate son—when God declared them a nation at Mt.Sinai, three months after he delivered them from Egypt. Thus, God redeemed them before he adopted them. He redeemed them in order to adopt them.
Of course, Israel repeatedly failed in its sonship by rejecting the Father’s love, replaying the story of Adam’s rebellion. God’s mission to bring many wayward and rebellious sons home to glory seemed doomed. Yet through Israel, God’s corporate son through adoption, the eternal and perfect Son would be sent to redeem humanity, thereby preserving God’s perfect plan.
3. Jesus (Galatians 4:4-6)
“But when the fullness of time had come, God sent forth his Son, born of woman, born under the law, to redeem those who were under the law, so that we might receive adoption as sons.” Here, Paul identifies adoption as the grand purpose or objective of redemption, and he could not have written it more clearly: “…so that we might receive adoption”! Once again, adoption shows up at a watershed moment within the unfolding story of redemption. Just as God redeemed Israel in order that he might adopt them, so also has God redeemed us in order that he might adopt us! Redemption is not the end of God’s work. Adoption as sons is.
4. New Heavens & New Earth (Romans 8:15, 22-23)
Finally, adoption is central to the end of redemption’s story. In verse 23, Paul writes, “And not only the creation, but we ourselves, who have the firstfruits of the Spirit, groan inwardly as we wait eagerly for adoption as sons, the redemption of our bodies.” Paul identifies our adoption. When the story of redemption reaches its intended goal, the Bible calls it “adoption.” On that climactic day the heavens and the earth will be transformed into our Father’s house. The renewed earth will become the place where we forever enjoy our Father’s love as his sons and daughters. Paul’s use of adoption in Romans 8 teaches us that missional living is not directionless living. Missional Christians daily fix their eyes on the climax of God’s work of adoption—God’s renewed heavens and earth.
So we see that Paul teaches that God does not merely redeem us—through adoption he brings us into the warmth, love, and gladness of his own family. Redemption was never intended to be God’s “be-all and end-all” work of grace. God redeemed us in his Son so that he might love us and delight in us even as he loves and delights in his eternal Son… Adoption is God’s act of making room within his triune love for prodigals who are without hope, and providing them with homes in this world and the world to come. This is the story of adoption.
[Cruver notes: The occurrences of "adoption" in Paul's writing's can be easily arranged chronologically along the timeline of the story of redmption... Dr. Timothy Trumper fleshes this out wonderfully in "A Fresh Exposition of Adoption: An Oultine," in Scottish Bulletin of Evangelical Theology 23 (2005) pp. 60-80]