Paul elaborates on the wonderful Biblical truth of adoption. Those who trust in Christ receive the Holy Spirit and are freed from slavery to sin, they are adopted as a child of God and become an heir to eternal life.

Galatians 4:1–7

Sons and Heirs

4:1 I mean that the heir, as long as he is a child, is no different from a slave,¹ though he is the owner of everything, 2 but he is under guardians and managers until the date set by his father. 3 In the same way we also, when we were children, were enslaved to the elementary principles² of the world. 4 But when the fullness of time had come, God sent forth his Son, born of woman, born under the law, 5 to redeem those who were under the law, so that we might receive adoption as sons. 6 And because you are sons, God has sent the Spirit of his Son into our hearts, crying, “Abba! Father!” 7 So you are no longer a slave, but a son, and if a son, then an heir through God.

Footnotes

[1] 4:1 For the contextual rendering of the Greek word doulos, see Preface; also verse 7
[2] 4:3 Or elemental spirits; also verse 9

(ESV)