Q: What is adoption?
A: Adoption is an act of God's free grace, whereby we are received into the number, and have a right to all the privileges of, the sons of God.
1 John 3:1 See what kind of love the Father has given to us, that we should be called children of God; and so we are. The reason why the world does not know us is that it did not know him.
This truth of adoption has, to me, been one of the most amazing truths of Scripture. Think about this. God not only justifies us by the blood of his Son Jesus Christ, but now, having been justified, we are brought into his family, adopted as sons and daughters.
That word, "adoption", is a strong word. Families who have adopted children show us just how powerful this is. An adopted child is a child of that family. He or she does not hold some kind of secondary status in the eyes and hearts of the parents simply because the child is not of the same biological strain as their "natural" children. No, the child is their child, plain and simple. The adopted child is shown the same love, the same compassion, the same concern, and has the same benefits and inheritance as the natural born child. The child truly and really is a part of the family in every single way.
And this is how it is with us, as we're brought into the family of God. Our Heavenly Father does not hold us in contempt for our sin. He brings us in, justifies us by the righteousness of his only begotten Son, Jesus Christ, and now he gives us all the same benefits as his own Son. We do not hold a secondary status, we are not seen as "lesser children", we are not shown a lesser degree of love, compassion, and concern, no brothers and sisters, we truly are the children of God! The Father is our Father! The Son is our brother, and his inheritance will be our inheritance! Is this not simply remarkable?