The Scriptures teaches that Salvation is of the Jews. The Jews were God's people and all else were Gentiles.
So we came no where close in being God's sons & daughters.
God rose up a man, a man that became the Apostle to the Gentiles to open up the way for the Gentiles to partake in a Dispensation what is known as Grace, "The Dispensation of Grace".
In the Dispensation of Grace, God is making the Gentiles His own through Christ.
("And if you be Christ's, then you are Abraham's seed") (Gal.3:29)
Under this Grace, God would now bring in many sons & daughters into His kingdom through Adoption. ("That the Gentiles should be fellowheirs, and of the same body...") (Eph.3:6)
WHAT DOES ADOPTION MEANS TO US
As His children we enjoy All the privileges, benefits, rights as the only Begotten Son of the Father. Christ is the Son by nature and is Eternal Being, we become the sons & daughters by Adoption in time through Grace.
For this reason have the Fathers given us His Spirit whereby we have the right and authority to call Him Father, Abba.(Rom.8:15)
We are not yet born of God literally ("What is born of flesh is flesh, what is born of Spirit is spirit") , and yet while in the flesh, we......
"Behold what manner of love the Father has bestowed upon us that we should be called the sons of God" [NOW]
SERVANTHOODUnder the Law we were servants, under Grace, we became the sons & daughters of God through Adoption by His Spirit testifying that we are children legally.
Who we are as Adopted
1) Joint heirs with the Son. (Tit.3:7; Js.2:5
2) We bear the Sons title, Christians
3) We are made kings unto the Father. [You cannot be a king without a kingdom]
4) We have become Strangers and Foreigners in the earth representing our Father and our Heavenly Country in this world.