For those who are led by the Spirit of God are the children of God. The Spirit you received does not make you slaves, so that you live in fear again; rather, the Spirit you received brought about your adoption to sonship. And by him we cry, Abba, Father. Romans 8:14-15 NIV

God is the Father of all in the sense that he created all and his love and providential care are extended to all (Mt 5:45). But not all are his children. Jesus said to the unbelieving Jews of his day, “You belong to your father, the devil” (Jn 8:44). People become children of God through faith in God’s unique Son (Jn 1:12), and being led by God’s Spirit is the hallmark of this relationship.

The Greek word for adoption into sonship occurs four other times in the [New Testament] (Romans 8:23; 9:4; Gal 4:5; Eph 1:5). Adoption was common among Greeks and Romans, who granted the adopted son all the privileges of a natural son, including the inheritance rights. Christian are adopted sons by grace; Christ, however, is God’s Son by nature.

Every good and perfect gift is from above, coming down from the Father of the heavenly lights, who does not change like shifting shadows. James 1:17 NIV 

God is the creator of the heavenly bodies, which give light to the earth, but, unlike them, he does not change.

Yet to all who did receive him, to those who believed in his name, he gave the right to become children of God—children born not of natural descent, nor of human decision or a husband’s will, but born of God. John 1:12-13 NIV

Membership in God’s family is by grace alone – the gift of God (Eph 2:8-9). It is never a human achievement, as v. 13 emphasizes; yet the imparting of the gift is dependent on human reception of it, as the words “did receive” and “believed” make clear.

The “children of God” (v. 12) have been given a new openness to and relationship with God that was not theirs as a result of their natural birth (John 3:3, 5; 2Co 5:17; Gal 6:15; Titus 3:5).