James Dunn points out in his commentary that this section restates many of the same points in 3:23-29:
•We were held captive under the law (23)
•Imprisoned until the coming faith would be revealed (23)
•But now that faith has come (25)
•We are no longer under a guardian (25)
•You are all sons of God (26)
•You are Abraham's offspring, heirs according to promise (29)
•No different from a slave (1)
•Under guardians and managers until the date set by his father (2)
•But when the fullness of time had come (4)
• To redeem those who were under the law (5)
•Adoption as sons (5)
•So you are no longer a slave, but a son, and if a son, then an heir through God (7)
1 I mean that the heir, as long as he is a child, is no different from a slave, though he is the owner of everything,
2 but he is under guardians and managers
Cf. 3:24, the Law was a paidagogos.
until the date set by his father.
This continues Paul’s argument from salvation history, focusing on the primacy of the promise and the temporary nature of the Law.
3 In the same way we also, when we were children,
Though it is not possible to determine for sure what Paul means by “we,” I think the context favors the view that when he speaks in the first person he is referring to his fellow Jews, in contrast to Gentiles.
were enslaved to the elementary principles of the world.
“Elementary principles” can have a wide variety of meanings, but probably the Law is in view as the initial ABCs of God’s revelation (cf. Heb. 5:12).
The ESV obscures this point by rendering this “enslaved to the elementary principles,” rather than “under” (as the KJV, NKJV, NASB, and NIV do). The key word of “under” has consistently been used of the Law (3:23; 3:25; 4:2).
4 But when the fullness of time had come,Now that the “date set” has been reached, “the fullness of time” has arrived.
God sent forth his Son,
Through the entire section of 3:15-4:7 Paul emphasizes the idea of offering and sonship.
born of woman,
This may connect Christ with humanity in general.
born under the law,
This identifies in relation to Israel specifically.
5 to redeem those who were under the law,
This is similar to Paul’s statement in 3:13-14 that Christ redeemed us from the curse of the Law by becoming a curse for us.
so that we might receive adoption as sons.
This phrase could refer to all people, but I again tend to think it refers to Jews. Paul speaks of Israel’s “adoption” as sons in Rom. 9:4.
6 And because you are sons, God has sent the Spirit of his Son into our hearts,
This continues Paul’s emphasis on our solidarity with Christ. In the Son we become sons and share with Him and His Spirit.
crying, “Abba! Father!”
This was the prayer of Jesus in the garden (Mark 14:36). Now, because we are sons with Him, His prayer becomes ours.
7 So you are no longer a slave, but a son, and if a son, then an heir through God.
The train of though in 4:1-7 is very similar to Romans 8:15-17.