Paul says God sent his Son “to redeem those who were under the law, so that we might receive adoption as sons.” He adds that God sent “the Spirit of his Son” into hearts crying “Abba! Father!” (Galatians 4:4–6).
In Galatians 4:1–7 Paul compares a child heir to a slave: though the child owns the estate in principle, he lives under managers until the set time. He says this pictures “us” in an earlier stage, trapped under basic powers that ran life. This section continues Paul’s argument from the immediately previous discussion about the promise to Abraham and the later arrival of the law (Galatians 3:23–29). He has been explaining an “earlier stage” versus a “mature stage,” and how the law functioned like temporary supervision.
Paul’s core contrast is between status in principle and experienced freedom in practice. A minor can be the true heir and still live under strict supervision, “no different from a slave” (verses 1–2). Paul applies that picture to an earlier stage of God’s people: “we” were once enslaved “under the elements of the world” (verse 3).
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with Galatians 4:4-6, then read the surrounding section so the answer stays connected to the passage's flow.
4But when the fullness of the time came, God sent forth his Son, born to a woman, born under the law,
5that he might redeem those who were under the law, that we might receive the adoption of sons.
6Because you are sons, God sent forth the Spirit of his Son into our hearts, crying, "Abba! Father!"