Scottish theologian John Murray reflects on the Christian’s spiritual adoption:
The great truth of God’s fatherhood and of the sonship which bestows upon men is one that belongs to the application of redemption. It is true in respect of all men no more than are effectual calling, regeneration, and justification.
God becomes the Father of his own people by the act of adoption. It is the marvel of such grace that constrained the apostle John to exclaim, ‘Behold what manner of love the Father has bestowed upon us that we should be called children of God’ (1 John 3:1). And to assure his readers of this privilege as a present possession and not simply a hope for the future he adds immediately, ‘and we are.’ To indicate the cleavage which this status institutes among men he continues, ‘On this account the world does not know us, because it did not know him.’
Lest there should be any doubt regarding the reality of the sonship bestowed he insists, ‘Beloved, now we are the children of God.’ (ver. 2). John had pondered and learned well the words of the Lord himself when he said, ‘he that loveth me shall be loved by my Father….If a man love me he will keep my words: and my Father will love him, and we will come unto him, and make our abode with him’ (John 14:21,23).
And now in writing his first epistle his heart overflows with wonderment at this donation of the Father’s love, ‘Behold what manner of love the Father hath bestowed on us.’ It is specifically the Father’s act of grace. John could not get over it and he never will. Eternity will not exhaust its marvel.
John Murray, Redemption Accomplished and Applied (Grand Rapids, MI: Eerdmans, 1955), 136.