Adoption is a legal process that creates a parent-child relationship between individuals who are not biologically related. The adopted child is entitled to all the rights and privileges that would belong to a natural child of the adoptive parents.
Paul writes that Christians have been adopted by God (Romans 8:15, Galatians 4:5 and Ephesians 1:5). Paul takes the legal concept of adoption from first century AD Roman law and uses it to illustrate the relationship that Christians now have with God. Under Roman law, a man who had no son could take anyone, even one of his slaves, and make him his son. The person so adopted took the name of the father and in all respects was regarded and treated as a son, no different than if he was the biological offspring. The same holds true with adoption today. When I adopted my daughters, the judge made clear to my wife and I that in the state of California, once we signed the adoption papers, the adoption could not be undone.
Our children’s status is stronger than if they were our biological offspring. The state of California will not allow us to disown them. The state of California requires that they will inherit our property. Thus, the fact that we have been made children of God as Christians clarifies the nature of our relationship with God and gives us confidence in that relationship. Christians do not have to live in fear that they can somehow destroy that relationship. The relationship is stronger than that between parents and their biological offspring.
Paul points out that, just as when a slave was adopted and made a son, so we, like that Roman slave, are no longer slaves who must say “Master.” Now we are His children, and can call him “Father” (Romans 8:15). The Christian’s status, his or her relationship to God, has been permanently transformed.
Other metaphors that the New Testament authors use to describe the standing of the Christian with God are just as radical. The church is the bride of Christ (Ephesians 5:25), the body of Christ (1 Corinthians 12:27), and Jesus tells us that Christians are not servants, but friends (John 15:15).
Other examples of adoption in the Bible are the adoption of Moses by Pharaoh’s daughter (Exodus 2:10), Esther’s adoption by Mordecai (Esther 2:7) and God’s adoption of the people of Israel (Exodus 4:22, Deuteronomy 7:6, Hosea 11:1, and Romans 9:4).