Are adopted (rather than biological) children in a Christian family part of the covenant? What Bible references can you suggest for your view?
The short answer is, “Yes! Absolutely!”
Salvation in neither the Old Testament nor the New Testament is biological. Sin is biological, that is, it is passed from father to son on account of Adam’s guilt, but grace is not.
We begin with Abraham, the father of the faithful. God promised to save Abraham’s seed, by which he meant to save his elect children in Christ. Galatians 3:16 makes this absolutely incontrovertible: “Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed.” If only the biological children of Abraham could be in the covenant, woe unto us! We would not be in the covenant, but since Abraham’s seed is Christ’s spiritual seed, we Gentiles can be and are included in the covenant: “Know ye therefore that they which are of faith, the same are the children of Abraham” (Gal. 3:7). “For ye are all the children of God by faith in Christ Jesus” (Gal. 3:26). “And if ye be Christ’s, then are ye Abraham’s seed, and heirs according to the promise” (Galatians 3:29).
When God gave Abraham the sign and seal of the covenant (see Rom. 4:11), he did not restrict it to Abraham’s biological children: “And he that is eight days old shall be circumcised among you, every man child in your generations, he that is born in the house, or bought with money of any stranger, which is not of thy seed” (Gen. 17:12). The issue is not biology. The issue is Abraham’s household.
Consider what adoption is. A couple, often childless, or desiring more children, choose to take a child into their home. They choose to give that child all the privileges of being a member of their family. They give that child the right to live with them, to eat with them, and to be loved by them. They treat that child exactly as they treat all their other children. That child has the right to call the woman who adopted him “Mom” and the man who adopted him “Dad.” It would be a denial of all that adoption is, if that couple locked their adopted child in the basement, or made him sit in the corner by himself, while they lavished love upon only their biological children.
The main issue with adoption is this: the legal process takes time. That child is not adopted until all the paperwork is finished and signed, and a court is satisfied. But once adoption is finalized, the child has all the privileges, rights and responsibilities of any other child.
If that child is adopted by Christians, he has the same privileges, rights and responsibilities of any other covenant child. And that means that as a covenant child, he is as much as covenant child as any biological child of any other church member. That means that that adopted child, that adopted covenant child, will be baptized, catechized and instructed with all the other children. We will not have separate categories in the church for biological children and adopted children. (One practical point: the consistory will sometimes delay baptism of such children, because they need to make sure that the adoption process is finally and formally over before the children are officially adopted. Once the adoption papers are signed, however, the application for baptism can usually proceed as normal).
In fact, since not all biological children are in the covenant, the biological must never boast against the adopted children. Absalom and Adonijah were David’s biological sons, but they were not true sons, unlike Mephibosheth, whom David adopted. There are biological sons, born to Christians, who rebel, and have to be cut off by church discipline, while adopted sons, taken from outside, prove to be faithful members of the church.
Is this not what happened throughout Israel’s history? When a pagan renounced idolatry and was adopted into Israel, was he not circumcised and given access to the spiritual privileges of life in Israel? Did he not become an Israelite indeed? Was he not embraced by God in his covenant? One need only think of Uriah the Hittite as an example of this.
That is our salvation. We are adopted children of God. God has only one eternal and natural, or only begotten Son, Jesus Christ. When God adopts us, he makes us his children indeed. he makes us his heirs, co-heirs with Jesus Christ himself. He sends his Spirit into our hearts, so that we cry, “Abba, Father” (see Rom. 8:14–17; Gal. 4:4–7). We are born “not of blood, nor of the will of the flesh, nor of the will of man, but of God” (John 1:13).
The “adoption process” for our salvation meant that God’s firstborn Son, Jesus Christ, sacrificed himself on the cross to atone for our sins. We are legally declared to be the sons and daughters of God because of what Jesus did. Our adoption papers, as it were, are signed in the blood of Jesus Christ.
Never will God say to us, his adopted children: “I love you less than I love my real Son, Jesus Christ.” Never will he say, “My Son, Jesus Christ, is in my covenant, but you, technically, are only adopted sons. You are secondary sons.” Never will he say, “I have an inheritance for my real Son, Jesus, and a secondary, lesser inheritance for you.” Never will we eat the crumbs under the table, as lesser sons, while Jesus, the real Son, feasts at his Father’s table.
And if God lavishes such love on us, we will not lavish less love and acceptance (less than full acceptance) upon the adopted children of Christian parents in the church.
We are co-heirs, sons with Christ! What a wonder of grace!