Before Christ, we were “children of wrath” by nature (Eph. 2:3). However, those upon whom God bestows His saving grace become the “children of God.” The Apostle Paul describes this process as Adoption. "Adoption” is the work of the Holy Spirit whereby the believing sinner becomes a member of God’s family, with all the privileges and obligations of family members.
The word adoption in the New Testament means "to place as an adult son." It was a term used in the Roman legal practice in the Apostle Paul’s day referring to a legal action by which a person takes into his family a child who is not his own, with the purpose of treating him as and giving him all the privileges of a biological son. An adopted child was legally entitled to all rights and privileges of a natural-born child. Children could always be fostered, but adoptions was permenant. In adoption, the family was able to preserve the family name, and the adoptee got a new father, a new family, a new name, and a new identity.
Paul uses "adoption" to illustrate the act of God giving a believing sinner, who is not His natural child, a position as His adult son in His family. The emphasis is on the legal position of the child of God. He now has a new father, a new family, a new name and a new identity.
God pre-determined it to be this way!
Ephesians 1:5, "having predestined us to adoption as sons by Jesus Christ Himself, according to the good pleasure of His will.
It brings God great pleasure that He is your Father and that you are His son! What a great privilege it is for you and I to be the absolute possession of the Father! We have already, as believers in Christ, been placed in the family of God and are led by the Holy Spirit as the adult sons of God.