Salvation is adopted sonship

This post continues a series in the book Life in the Trinity by Donald Fairbairn. For other posts in the series, click a number: 1234678.

Fairbairn equates salvation with adopted sonship by which we, through the Holy Spirit, share in Jesus' own relationship with his Father. God adopted humanity as his own dearly loved children (Gal 4:4-6) through the incarnation, birth, life, death, resurrection and ascension of his "only begotten Son", Jesus Christ (see John 1:18, KJV). In union with Jesus, humanity is embraced, forgiven, reborn, exalted and through the power of the Holy Spirit given to share in the Son's unimpeded fellowship with his Father. Note these comments from Fairbairn:
The Son has become human in order to make himself our adopted brother, so that we, having become his adopted sisters and brothers, could then become the adopted daughters and sons of his natural Father, God. The Son by nature has made us sons and daughters by grace. (p136)
Salvation is our sharing by adoption in the Son's own relationship to the Father. Because salvation is Christ, then only Christ can give himself to us. Only the one who is naturally the Father's Son, who has from all eternity shared in loving fellowship with the Father, is able to grant us participation by adoption in his own relationship to the Father.... The reason salvation cannot be earned is that salvation is adopted sonship. (pp136-7)  
The incarnation was the movement of God that made it possible for human beings who had lost their relationship with God to be restored to that fellowship again.... We are not sons and daughters by nature and never will be, but through the grace of the incarnation, we are given anew the fellowship that the natural Son shares with his Father. (p138)
To understand the nature of the incarnation, and how it accomplishes the adoption of humanity into the triuine life, it's vital to understand the dual nature of Jesus. He is not merely a human in whom God dwells, but...
...God the Son living personally on earth as one of us... Only the Son by nature could make us sons and daughters by grace, so in order for us to be saved, the natural Son had to come personally from heaven to earth through the incarnation. He did this, the [early] church proclaimed, by taking a human nature into himself, that is, by assuming a human set of characteristics and components into his own divine person to go along with the divine characteristics (that is, the divine nature) he had eternally possessed.... He was God the Son who became man while remaining God. (p142)
Jesus is ONE person: God the Son. He came down from heaven and united humanity to himself. And thus with the incarnation, this one person, the Son of God, now (and forever) possesses both divine and human natures. The stunning truth is that there is (and forever will be) a human in the Trinity. By grace, in union with Jesus, we share this human place in the triune fellowship of the Father, Son and Spirit.

In the life of this God-man, Jesus Christ, we see two things:
  1. What it looks like for God to share in the love and life of the Trinity
  2. What it looks like for a human to share in that love and life...
...a life [that is] characteristic of the age at the end of history when God's purposes will be fulfilled. It is a kind of life in which we share in the fellowship between the Father and the Son, just as humanity did at creation before the Fall. (p149)
In his humanity, Jesus lives perfectly on our behalf as one of us: He "obeys whereas Adam disobeyed, trusts where Adam failed to trust, resists temptation whereas Adam succumbed" (p154). Whereas Adam headed the human race into sin; Jesus (who replaced Adam as head of humanity) led us back to God. As noted by Irenaeus, Jesus, serving as our representative and substitute, passed through every stage of human life, restoring communion with God each point along the way (p154-5). As we trust Jesus, we participate as adopted sons and daughters of God in the perfect human life that he lives on our behalf in fellowship with the Father and the Holy Spirit. In Jesus, our salvation, which is our sharing through the power of the Holy Spirit in his Sonship, is established and forever secure!