But when the fullness of the time had come, God sent forth His Son, born of a woman, born under the law, to redeem those who were under the law, that we might receive the adoption as sons. And because you are sons, God has sent forth the Spirit of His Son into your hearts, crying out, “Abba, Father!”
Sonship is more than new birth. By spiritual birth we become children of God. This has been true of believers in all dispensations. But now by the reception of the Holy Spirit, who is the Spirit of adoption, we become sons. This is the distinctive blessing of the present dispensation of grace. Old Testament saints were as infants. New Testament Christians are sons who have come of age and are joint heirs with Christ. We are all children of God by the second birth and sons of God by adoption. This is what is unfolded here in Galatians, and also in Romans 8:14–17. In Roman law all born in the family were children, but only those legally adopted were reckoned as sons.
“Abba,” Father—thus we call Thee,
(Hallowed name!) from day to day;—
’Tis Thy children’s right to know Thee,
None but children “Abba” say.
This high honor we inherit,
Thy free gift, through Jesus’ blood;
God the Spirit, with our spirit,
Witnesseth we’re sons of God.
H. A. Ironside, The Continual Burnt Offering: Daily Meditations on the Word of God (Neptune, NJ: Loizeaux Brothers, 1994), 294.