Life for both the Jews and the Gentiles outside of Christ was bondage in many ways, but Paul speaks of them being under the “elemental spiritual forces” (Galatians 3:3, 9) which he characterizes as “weak and miserable” (v. 9). But when the time is ripe, God sends His Son who fully subjects Himself to the realities experienced by His people (the flesh and the law). He does this that He might redeem “those under the law, that we might receive the adoption to sonship” (v. 5). Here again, we come across an interesting twist. It’s a little surprising that Paul speaks of Jewish people receiving “adoption to sonship.” Weren’t they already God’s covenant people?
Dunn offers the explanation that early Roman law allowed for a son who went into slavery to be bought back by his father. This redemption would restore him to the family and sonship. Thus, he would go from slavery to adoption. Perhaps that’s the figure that Paul borrows here.
More likely is the idea that the adoption figure is employed to emphasize the dramatic change of status they underwent in going from the law (slavery-Romans 7:14) to Christ. Hosea 11:1ff speaks of God adopting Israel through the events of the exodus. It’s not that they didn’t belong to Him before the exodus (think of the promises made to Abraham, Isaac, Jacob and Joseph), but their deliverance from Egypt, the receiving of the law, the Shekinah presence—all of these represented a new status that Hosea speaks of as sonship for the nation. I think Paul is doing the same thing here to mark what has happened to them through Christ. It is wrong to think of the Christian faith as not Judaism 2.0, much less something that needs anything added to it.
But he doesn’t stop there. “Because you are His sons, God sent the Spirit of His Son into our hearts, the Spirit who calls out ‘Abba, Father.’” Notice how Paul now addresses the Galatians directly by using the pronoun “you.” He wants them to understand in no uncertain terms that Christ has brought them into sonship and as a consequence they receive His Spirit which brings not only intimacy with God, but unity with Jewish disciples—they are all sons who share the same Spirit. They are all receiving the promise made to Abraham (v. 7).