Slaves were set free to enjoy the full rights of sons only because God acted in history: when the time had fully come, God sent his Son. This reference to the time of God's action in history is directly related to the time set by his father (v. 2) in the previous illustration and concludes a whole string of references to God's time schedule: "until the Seed . . ." (3:19); "before this faith . . . up until faith" (3:23); "now that faith . . . we are no longer . . ." (3:25). When God sent his Son, the former period of universal slavery ended; a new era of freedom was inaugurated.

God's plan of salvation cannot be understood merely in static terms as a logical system of ideas: revelation, God, human nature, Christ, salvation, church. God's redemptive work must be understood in the framework of his actions in history. God gave an irrevocable promise to Abraham; 430 years later God gave the law through Moses; at a time God had set, he sent his Son. The relationship of these acts of God in history provides the framework for understanding the redemptive work of God. Of course this does not mean that we should abandon systematic theology; we can develop logical expositions of the meaning of salvation. But we should always remember that the narrative structure of God's work in history is the substructure of all truly biblical theology.

The confusion of the Galatian Christians was the result of their failure to understand the narrative structure of the redemptive work of God. In their attempt to inherit the blessing promised to Abraham by keeping the Mosaic law, they failed to understand that the Mosaic law had been given 430 years after the Abrahamic promise and could not change the terms of the promise or be a condition for inheriting the promised blessing (3:15-18). In their attempt to make progress in their spiritual life by observing the law after believing the gospel, they failed to understand that supervision under the law ended when faith in Christ came (3:23-25).

At the center of this narrative framework is the narrative of the gospel story itself: God sent his Son, born of a woman, born under law, to redeem those under law (4:4-5). Here we have a simple confessional statement of the essence of the gospel story: the incarnation and birth of Christ, his perfect life of obedience under the law, and his redemptive death on the cross.

The phrase God sent his Son is taken by some interpreters as merely a reference to the prophetic mission of Jesus. As the prophets of old were sent by God, so Jesus was sent by God for a special redemptive mission. The background may be found in the parable Jesus told about the wicked tenants of the vineyard (Mk 12:1-12): the owner of the vineyard (God) first sent messengers (prophets), who were killed by the tenants (Jewish leaders); then he sent his own son (Jesus), who was also killed. But in light of Paul's other references to the preexistence of the Son (see 1 Cor 8:6; Phil 2:5-8; Col 1:15-17), we may also see here an affirmation of the deity of Jesus. Before the incarnation, the preexistent Son was commissioned by God to set slaves free and make them children of God.

The next phrase, born of a woman, points to the incarnation and full humanity of Jesus. The Son of God was sent to be one with us in our humanity. He was God's Son and he was Mary's son—the one and only God-man. He was also born under law. The phrase under law cannot mean legalism, keeping the law to earn salvation. Jesus certainly did not live his life under the misconception that he had to keep the law to earn his salvation. To be born under law means to be born a Jew under obligation to keep the requirements of the Mosaic law. From his circumcision eight days after his birth to his celebration of Passover with his disciples just before his death, every detail of Jesus' life was under the direction of the law. His perfect obedience to God the Father, as God's Son born of a woman, fulfilled all the requirements of the law. God's Son took our place as a human being to offer a perfect obedience to God on our behalf.

To be born under law also means to experience the curse of the law against all who fail to observe all that the law requires (see 3:10). Although Jesus did fulfill all the requirements of the law, he still experienced all the conditions of sinful humanity under the curse of the law. He was subject to temptations, suffering, loneliness, and finally, on the cross, God-forsakenness and death.

The twofold purpose of the Son's full participation in our humanity, his perfect fulfillment of the law and his experience of the curse of the law on our behalf is given in the next two phrases: to redeem those under the law, that we might receive the full rights of sons (v. 5). Christ is uniquely qualified to fulfill these two purposes. Because he is the Son of God, he is able to give the position and rights of his sonship to sinful people. Because he became fully human, he is able to represent and redeem all humankind. And because he rendered perfect obedience to God and bore the curse of God against the disobedient, he is able to redeem those under the law. If being under law means being under obligation to keep the law and under the curse of the law for not keeping it, then to redeem those under the law means to set them free from both the obligation to keep the law and the curse of lawbreaking. When Paul says that Jesus was born under law, to redeem those under law, he means, as Calvin puts it, that "by putting the chains on himself, he takes them off the other." By taking the obligation and curse of the law upon himself, he set us free from both the obligation and the curse of the law.

The two verbs in verse 5, redeem and receive, present both sides of our relationship with God: God has already acted in history to set us free; for our lives to be changed by his action we need to respond in faith. Our response to God's action is depicted here as receiving the full rights of sons. This phrase in the NIV is a good translation of a legal term that means "adoption as sons." Adoption was defined by Roman law and widely practiced in Roman life. Several Roman emperors adopted men not related to them by blood in order to give them their office and authority. When a son was adopted, he was in all legal respects equal with those born into his new family. He had the same name, the same inheritance, the same position and the same rights as the natural-born sons. God sent his Son, who by his divine nature was the Son of God, in order that we, who are not his children by nature, might be his children by adoption and thus receive the full rights of sons. We have the same name, the same inheritance, the same position and the same rights as the one who is Son of God by virtue of his divine nature.

There is a shift in Paul's images here from the picture of a son who is treated like a slave until he reaches a certain age (vv. 1-2) to the picture of a slave who becomes a son by adoption (v. 5). The first picture clarifies the contrast between the two stages of redemption in history. The sending of the Son concluded the stage of slavery under law and inaugurated the new era when sons receive their inheritance. The second picture focuses on the nature of sonship itself. We are adopted as God's children by the sending of the Son of God.