“By adoption the redeemed become sons and daughters of the Lord God Almighty; they are introduced into and given the privileges of God’s family…
Adoption, as the term clearly implies, is an act of transfer from an alien family into the family of God Himself. This is surely the apex of grace and privilege.
We would not dare to conceive of such grace far less to claim it apart from God’s own revelation and assurance. It staggers imagination because of its amazing condescension and love.
The Spirit alone could be the seal of it in our hearts. ‘Eye hath not seen, nor ear heard, neither have entered into the heart of man, the things which God hath prepared for them that love him. But God hath revealed them unto us by his Spirit: for the Spirit searcheth all things, yea, the deep things of God’ (1 Cor. 2:9, 10).
It is only as there is the conjunction of the witness of revelation and the inward witness of the Spirit in our hearts that we are able to scale this pinnacle of faith and say with filial confidence and love, ‘Abba Father!’…
It is the same Person who is the Father of the Lord Jesus Christ in the ineffable mystery of the trinity who is the Father of believers in the mystery of His adoptive grace.
God the Father is not only the specific agent in the act of adoption; He also constitutes those who believe in Jesus’ name His own children.
Could anything disclose the marvel of adoption or certify the security of its tenure and privilege more effectively than the fact that the Father Himself, on account of whom are all things and through whom are all things, who made the captain of salvation perfect through sufferings, becomes by deed of grace the Father of the many sons whom He will bring to glory?
And that is the reason why the Captain of salvation Himself is not ashamed to call them brethren and can exult with joy unspeakable, ‘Behold I and the children whom God hath given to me’ (Heb. 2:13).”
–John Murray, Redemption: Accomplished and Applied (Grand Rapids, MI: William B. Eerdmans Publishing Company, 1955), 132, 134, 140.