Adoption is one of those doctrines that warms and encourages the soul and needs to be dwelt upon. It is also deeply foundational to who we are as united to Christ. J.I. Packer famously wrote (and Garner is quick to quote) that if he could summarize the New Testament in three words it would be “adoption through propitiation.”
This book is a challenging and academic read, one that is good for enhancing, deepening and poking at our gospel perspectives, while keeping Christ central.
In Garner’s first section of the book, he lays the adoption foundation -“Securing a family of adopted children occupied the mind of God since before the world’s origins…God purposed adoption, God accomplished adoption, and God applies adoption.”  After a brief survey of the concept of adoption in early church history and culture, Garner focuses on the Pauline references to huiothesia – the Greek term (literally “son-placing”) for adoption which the Apostle uniquely uses for spiritual (not social) adoption.
In the second section, the author dives into the specific texts exegetically and theologically. Ephesians 1:3-6 [“…God the Father…predestined us for adoption to Himself as sons thru Jesus Christ…”] As Garner wisely puts it “the opening words of Ephesians affirm, without the all-wise counsel and eternal purpose in the mind of God, redemption would have never happened.” Amen! Praise be to God for his sovereign mercy and grace. Garners stresses, as Paul does in his letters that adoption is in Christ (en Christo) and that union with Christ is paramount to keep in central focus. Many things stem from this, but one I appreciated particularly was the connection between adoption and Christlikeness. Eph 1:4 says that he “chose us…to be holy and blameless.” We have a calling and a purpose therefore as his adopted sons and daughters – bring him glory by looking more like Jesus, through his abundant transforming grace.
The author brings in a redemptive-historical view of adoption when looking more closely at Galatians 4:4-7. [“…so you are no longer a slave, but a son…”] We see that adoption was not only sovereignly planned, but accomplished in Christ. As he powerfully writes “the stranglehold of the law and the power of it’s curse meet their defeat under the power of Christ and the cross…”  As a result, thru faith, we are no longer slaves to the law/sin – but we are adopted as sons in freedom! Romans 8:15-17 furthers the emphasis of accomplishment. [“…you have received the Spirit of adoption as sons…”] This is indeed a powerful and central point, once again tied to Christlikeness in practicality – “The Spirit of adoption empowers the believer for spiritual renovation by mortification of sin, and he accomplishes this empowerment in the mystical union with the Son by the Spirit, or as Paul puts it succinctly, by adoption.”  Through this mortification of sin we grow into the reality of our adopted sonship. 
Garner makes some big statements in this book, one of which he brings out in the context of Ephesians 1:4 to 1:11. [“…works all things according to the counsel of his will…”] “Or put in Pauline shorthand, adoption is the singular goal of redemptive history, an adoption that changes the state of the sons, the hearts of the sons, and even the bodies of the sons.”  I can’t say that I disagree with this statement, but the author is laying the groundwork for some bigger statements to follow.
Section 3 contains the significant disconnect I have with the book. While remaining faithful to the orthodox doctrine of the eternality of Jesus as the Son of God, Garner maintains that Jesus himself was adopted as the Son of God at His resurrection. This point he carries then for the rest of the book, but devotes a whole chapter to it in chapter 7. Again, Garners sets the theological foundation with boundaries – “That Christ is eternal Son does not mean, however, that there is therefore no progressive, functional dimension to his sonship.”  Quoting Dunn, he claims this was the adoptionist perspective of primitive Christian teaching “…to have regarded Jesus’ resurrection as the day of his appointment to divine sonship, as the event by which he became God’s son.”  This can be a dangerous perspective and I couldn’t help but take it as a thesis driven push point. It colored the rest of my interpretation of the book.
The author mainly relies on Romans 1:3-4 for textual support – ““concerning his Son, who was descended from David according to the flesh and was declared to be the Son of God in power according to the Spirit of holiness by his resurrection from the dead, Jesus Christ our Lord,” (Romans 1:3–4 ESV). The centrality of the argument is the ESV (and KJV, NKJV, and NASB) translation of horisthentos as “declared” which Garner (along with NIV and the new CSV BTW) claims is actually better ” appointed” – thus surmising that Christ was appointed the (adopted) Son at his resurrection. To be blunt, I can’t buy this, I don’t think it’s helpful, and again it can be dangerous. Citing support from Gaffin [“…the resurrection of Jesus is his adoption.”] he claims this nuanced interpretation warrants serious attention. 
Where it troubles me further is the connection made to biblical Christology and biblical soteriology. “To put it simply, without the human biography of Christ Jesus, capped by his own adoption as the Son of God, there is no salvation.”  – I would wholeheartedly agree with this statement, were it not for the singling out of Christ’s “adoption.”Hence, I cannot. We are saved by grace through faith in Jesus, I know the author agrees with that of course, but the addition of the adoption of Christ himself seems to obfuscate the overwhelming orthodox centrality of it. Highlighting my concern are statements such as “…there is no adoption of believers in Christ Jesus without the adoption of Christ Jesus.” As he continues to make the point, I find myself less and less convinced and more and more concerned. Don’t get too excited – I realize that Garner isn’t denying the eternal divine sonship of Christ, he is stating that “…at his resurrection, Jesus enters a new phase and new dynamic of sonship.” , but I’m at a loss as to why this nuance is emphasized for half of the book.
I appreciated Garner’s discussion of the ordo salutis and rescuing it from a forensic, stale, sequential view. He returns to highlight the importance of sanctification resulting from our adoption, and brings a balanced perspective to a sometimes over-emphasized justification. “Actual holiness is as important as declared holiness.”  AMEN! He expands the readers view of ordo salutis and it is appreciated and helpful. “The golden chain of salvation then comes to the redeemed not as consecutive links, but at once as a gloriously completed crown of divine filial grace.” Once again, AMEN! Having sat thru many extended dialogs on “which came first” this is very refreshing and helpful.
All in all, I found this book equally helpful and challenging, but one that should be read with a Berean mindset as the priority given to Christ’s own adoption should not be read without significant personal prayer, study, and thought.