“The gift of sonship to God becomes ours not through being born, but through being born again. ‘As many as received Him, to them He gave the power to become the sons of God, even to them that believe on His name: which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God’ (John 1:12-13)
Sonship to God, then, is a gift of grace. It is not a natural but an adoptive sonship, and so the New Testament explicitly pictures it. In Roman law, it was a recognized practice for an adult who wanted an heir, and someone to carry on the family name, to adopt a male as his son—usually at age, rather than in infancy, as is the common way today.
The apostles proclaim that God has so loved those whom he redeemed on the cross that he has adopted them all as his heirs, to see and share the glory into which his only begotten Son has already come.
‘God sent forth His Son… to redeem them that were under the law, that we might receive the adoption as sons” (Galatians 4:4-5): we, that is, who were ‘foreordained unto adoption as sons by Jesus Christ unto Himself” (Ephesians 1:5 RV).
‘Behold, what manner of love the Father hath bestowed upon us, that we should be called the sons of God… when He appears, we shall be like Him, for we shall see Him as He is’ (1 Jn 3:1-2).
You sum up the whole of New Testament teaching in a single phrase, if you speak of it as a revelation of the Fatherhood of the holy Creator. In the same way, you sum up the whole of New Testament religion if you describe it as the knowledge of God as one’s holy Father.
If you want to judge how well a person understands Christianity, find out how much he makes of the thought of being God’s child, and having God as his Father.
If this is not the thought that prompts and controls his worship and prayers and his whole outlook on life, it means that he does not understand Christianity very well at all.
For everything that Christ taught, everything that makes the New Testament new, and better than the Old, everything that is distinctively Christian as opposed to merely Jewish, is summed up in the knowledge of the Fatherhood of God.
‘Father’ is the Christian name for God. Our understanding of Christianity cannot be better than our grasp of adoption.”
–J.I. Packer, Knowing God (Downers Grove, IL: InterVarsity, 1973), 181-182.
