Have you ever considered why Scripture encourages us to call God our Father? What eternal truths does that simple title point to, and what does it teach us about the radical change God has wrought in the lives of those who love Him?
We began this series by considering the state of unrepentant man—hopelessly lost in his sin and condemned to suffer the due penalty of his sin. But as we saw, God graciously intervened, transforming His people by grace through faith, and fitting them for righteousness and an eternal home with Him. It’s appropriate, then, to conclude this series by considering the glorious reality of redeemed man’s new position in Christ.
Specifically, we’re going to look at a particular illustration Scripture regularly uses to describe our new relationship with God. In his book Slave, John MacArthur describes this beautiful, uplifting analogy:
That God, in His grace, would free us from sin and make us His slaves is a wondrous truth to comprehend. What a privilege to know and obey the heavenly Master! . . . And yet the Lord has bestowed an even greater distinction upon those who are His own.
Having delivered us from the destitution of sin, God not only receives us as His slaves—but He has also welcomed us into His household and made us members of His very family. He not only rescued us, purchased us, befriended us, and took us in; He has also adopted us, thereby transforming those who were formerly children of wrath (Ephesians 2:3) into the sons and daughters of righteousness. All of this is possible through the redemptive work of Christ, who is the “only begotten Son” (John 3:16), and the “firstborn among many brethren” (Romans 8:29).
The very term adoption is filled with ideas of compassion, kindness, grace, and love.  Slave, 154-155
A First-Century Illustration
Most of us are familiar with adoption in the twenty-first century—after all it’s a relatively common practice. But it wasn’t nearly as common in the world of the New Testament. To help us understand the full weight and vivid imagery of the biblical metaphor, John explains what adoption looked like in Roman society.
Though the formal adoption of slaves was somewhat uncommon, it was permissible under Roman law and did occur in certain instances. The extraordinary nature of the practice makes God’s adoptive love toward us all the more remarkable—in that He has done the unexpected by adopting all His slaves as His own children and naming us His heirs (Romans 8:17). In ancient Rome, the act of adoption immediately granted the former slave his freedom, permanently placing him into the family of his master. So also, as the adopted children of God, we have been set free from slavery to sin. Moreover, we can rest assured in knowing that we have been given a permanent place in the family of God.
Adoption, in Roman times, signified a new beginning: entrance into a new family such that all previous ties and obligations were broken. The adoption process consisted of several specific legal procedures. The first step completely terminated the adopted child’s social relationship and legal connection to his natural family. The second step made him a permanent member of his new family. . . .
Once the adoption was complete, the new son or daughter was then completely under both the care and control of the new father. The previous father no longer had any authority over his former child. In Roman households, the authority of the paterfamilias (“father of the family”) was final and absolute. And that authority extended to those adopted into the household, starting at the moment of their adoption.  155-157
So it is with us, as the Lord looks upon lost and wicked “children of wrath” (Ephesians 2:3), breaks the chains of our former master (sin—Romans 6:17), and removes us from the authority of our former father (the devil—John 8:44). All ties to our previous life are broken and we’re grafted into His eternal family and treated as if we had been there all along. From our heavenly Father’s perspective, no hint of our past life lingers, and none of the old animosity between us remains. We are His children, submitting to His authority and resting in His care.
As you might imagine, the benefits of such heavenly adoption are vast, as John MacArthur illustrates,
Because of our position in Christ, God now views us and treats us as He does His own Son—with infinite love. The Father cannot give anything but His best to His Son. Likewise, He will not give anything but His best to those of us who are in Christ—which is why we can “know that God causes all things to work together for good to those who love God, to those who are called according to His purpose” (Romans 8:28).  157-158
Reflecting on the everlasting blessings and privileges of heavenly adoption, D. Martyn Lloyd-Jones wrote,
If God has adopted you into His family, if you are a child of God, your destiny is secure, it is certain. . . . It is a guarantee. If God has taken me into the family I am not only a child, I am an heir, and nothing, and no one can ever rob me of the inheritance.  D. Martyn Lloyd-Jones, Great Doctrines of the Bible (Wheaton: Crossway, 2003), 189
And it’s not just the Father who welcomes us into the heavenly household. The writer of Hebrews describes how our spiritual adoption also shapes our eternal relationship to Christ. “For both He who sanctifies and those who are sanctified are all from one Father; for which reason He is not ashamed to call them brethren” (Hebrews 2:11).
Paul and Adoption
The apostle Paul would have been familiar with the method and meaning of adoption in Roman society, and he put the language of adoption to vivid use in his epistles. We’ll consider two poignant examples.
In his letter to the Galatians, he described how God’s spiritual adoption had set believers free from the rigid legalism of Judaism.
But when the fullness of the time came, God sent forth His Son, born of a woman, born under the Law, so that He might redeem those who were under the Law, that we might receive the adoption as sons. Because you are sons, God has sent forth the Spirit of His Son into our hearts, crying, “Abba! Father!” Therefore you are no longer a slave, but a son; and if a son, then an heir through God. (Galatians 4:4-7)
To the Romans, he emphasized how heavenly adoption sets us free from the slavery of sin and its eternal consequences.
For all who are being led by the Spirit of God, these are sons of God. For you have not received a spirit of slavery leading to fear again, but you have received a spirit of adoption as sons by which we cry out, “Abba! Father!” The Spirit Himself testifies with our spirit that we are children of God, and if children, heirs also, heirs of God and fellow heirs with Christ, if indeed we suffer with Him so that we may also be glorified with Him. (Romans 8:14-17)
In Slave, John MacArthur explains how those passages emphasize the importance and the value of our adoption into the family of God.
Though we were formerly enslaved to sin and the condemnation of the Law, we have been permanently liberated through our adoption into the family of God. As His adopted children, we enjoy the profound privilege of an intimate relationship with our heavenly Father, to whom we cry out with childlike affection, “Abba!”
A term of intimate endearment, Abba is an informal Aramaic term for “Father.” It expresses tenderness, dependence, and a childlike assurance that lacks any anxiety or fear. Jesus Himself used the term in the Garden of Gethsemane when He poured out His heart to His Father (Mark 14:36). That we would be allowed to address the Father in the same way Jesus did underscores the magnificent reality of our adoption. To be considered “heirs of God and fellow heirs with Christ” is a remarkable truth, and one that we should never take for granted.
To think that we, who were once the slaves of sin, the subjects of Satan, and the sons of disobedience, are now and forever the slaves of Christ, the citizens of heaven, and the children of God—such is the joy and wonder of salvation. As His enemies, we did not even deserve to be His slaves. Yet, He has made us both His slaves and His children. The incomparable reality of adoption is this: If God is our Master, then He is also our Father.  Slave, 159-160