J.I. Packer has aptly summarized the Gospel as “Adoption by grace.” In my favorite little intro to the Reformed tradition,  J. Todd Billings explains that God’s adoption of us in Christ, is not only a metaphor about our initial justification, but plays into the way we think of our sanctification:

While the metaphor of adoption begins as a legal act, it does not end there: it ends with membership in the household of God (Gal. 6:10; Eph. 2:19), with a calling to act into the reality of this new identity. God’s legal act of adopting into the family of God results in a new identity, in an eschatologically conditioned way. Thus, when we are given an identity in Christ, we are called to live into it. For example, the doxological opening of Ephesians 1 says that God “destined us for adoption as his children through Jesus Christ” (v. 5). As the blessings of being in Christ are unfolded in the following verses, Paul returns to the language of adoption and inheritance—that “in Christ we have also obtained an inheritance, having been destined according to the purpose of him who accomplishes all things according to his counsel and will, so that we, who were the first to set our hope on Christ, might live for the praise of his glory” (1:11–12, emphasis added). This new identity of one belonging to a new family in Christ is sealed by the Spirit in the verses that follow: “In him you also . . . were marked with the seal of the promised Holy Spirit; this is the pledge of our inheritance toward redemption as God’s own people, to the praise of his glory” (1:13–14). The adopted identity in Christ, sealed by the Spirit, leads to living “for the praise of his glory” (1:12), but also provides the ground for numerous ethical exhortations in Ephesians: the call to unity (4:13); to prayer (6:18); to speaking and living the truth in Christ (4:15, 21, 25; 6:14); to living in “love” rather than in anger, malice, and bitterness (4:21–5:1). All of these exhortations are to reflect the behavior of those who have been conferred a new adopted identity in Christ and who seek to live into this inheritance received as children of God in Christ.

In contrast to some theologians who have associated adoption only with justification, Paul’s overall usage of the adoption metaphor describes both the legal dimension of being transferred into God’s family and the transformative dimension of growing in God’s family. By associating adoption only with justification, theologians have sometimes tended to emphasize the legal at the expense of the transformative side of adoption. Trevor Burke has criticized certain Reformed scholastic thinkers, in particular, for making adoption a subset or benefit of justification without recognizing its distinct meaning. While Burke makes a good point, I suspect some of the reason for the confusion comes from the following: Theologians have often spoken about the act of becoming adopted as a forensic act, which is a valid point (as Burke agrees). But the forensic sense of becoming adopted does not exhaust the meaning of Paul’s metaphor, because the result of that act is that one is adopted to be a son or daughter of God, placed in the security of God’s family, and given a new identity to live into in an eschatologically conditioned way. Some theologians have thus been too quick to assume that the meaning of “adoption” is exhausted by the act of becoming adopted. Significantly for this chapter, however, this is not a mistake that John Calvin makes. Calvin uses the image of adoption as a way to describe the double grace of justification and sanctification received in union with Christ. Calvin understood that as an image for salvation, the act of becoming adopted is a legal, forensic action, but it has another dimension as well: as an image for the way Christians are to act as children of the Father who promises “to nourish us throughout the course of our life.” Indeed, the Spirit gives new life, displayed in love of God and neighbor, which “shows that the Spirit of adoption has been given to us (cf. Romans 8:15).”

–J. Todd Billings (2011-11-01). Union with Christ: Reframing Theology and Ministry for the Church (Kindle Locations 457-486). Baker Publishing Group. Kindle Edition.

Unsurprisingly, J.I. Packer has quite a bit to say about the way adoption transforms our identity. Towards the end of his chapter on the subject in his classic Knowing God, Packer summarizes some of the glories of adoption and gives us some questions to ask ourselves in light of this brilliant reality:

Do I, as a Christian, understand myself? Do I know my own real identity? My own real destiny? I am a child of God. God is my Father; heaven is my home; every day is one day nearer. My Savior is my brother; every Christian is my brother too. Say it over and over to yourself first thing in the morning, last thing at night, as you wait for the bus, any time when your mind is free, and ask that you may be enabled to live as one who knows it is all utterly and completely true. For this is the Christian’s secret of—a happy Life?—yes, certainly, but we have something both higher and profounder to say. This is the Christian’s secret of a Christian life, and of a God-honoring life, and these are the aspects of the situation that really matter. May this secret become fully yours, and fully mine. To help us realize more adequately who and what, as children of God, we are and are called to be, here are some questions by which we do well to examine ourselves again and again.

Do I understand my adoption? Do I value it? Do I daily remind myself of my privilege as a child of God?

Have I sought full assurance of my adoption? Do I daily dwell on the love of God to me?

Do I treat God as my Father in heaven, loving, honoring and obeying him, seeking and welcoming his fellowship, and trying in everything to please him, as a human parent would want his child to do?

Do I think of Jesus Christ, my Savior and my Lord, as my brother too, bearing to me not only a divine authority but also a divine-human sympathy? Do I think daily how close he is to me, how completely he understands me, and how much, as my kinsman-redeemer, he cares for me?

Have I learned to hate the things that displease my Father? Am I sensitive to the evil things to which he is sensitive? Do I make a point of avoiding them, lest I grieve him?

Do I look forward daily to that great family occasion when the children of God will finally gather in heaven before the throne of God, their Father, and of the Lamb, their brother and their Lord? Have I felt the thrill of this hope?

Do I love my Christian brothers and sisters with whom I live day by day, in a way that I shall not be ashamed of when in heaven I think back over it? Am I proud of my Father, and of his family, to which by his grace I belong? Does the family likeness appear in me? If not, why not?

God humble us; God instruct us; God make us his own true children.

—Knowing God, pp. 258-260

Soli Deo Gloria