Do you want to know how you can become an heir to God's promise, and receive the incredible blessings that come with it? If that is your heart's desire, then let Paul take you through the process. He begins by contrasting the present age of spiritual liberty in Christ with the past era of spiritual immaturity under the law. In order to explain, he uses the illustration of a family situation.
Christ's coming ushers in an era of spiritual liberty for all who turn to Him.
The young heir of his parents' estate will own it fully only when he comes of age. Until then, he is a minor and comes under the charge of guardians and trustees (Galatians 4:2). They not only hold the estate in trust, but also act as his tutors, hence subjecting the young heir to control and restrictions. Although he owns the entire estate, the child at this time is no better than a slave (v. 1). When he grows up and comes of age, however, he will be free from supervision, and the estate will be under his full control.
Likewise, we all were once under guardianship. Paul likens this period to slavery under the ″elementary principles of the world″ (v. 3 ESV). In the case of the Jews, this would have been bondage to their laws and traditions; for Gentiles, perhaps their pagan worship and rites. But that was before Christ came. This old order ended when God sent His Son at the time He had determined (vv. 2, 4). Christ's coming ushers in an era of spiritual liberty for all who turn to Him. He is the Son of God-the second person in the Trinity-and the Son of Man (″born of a woman″, v. 4), and one who though ″born under the law″ has kept the law perfectly (v. 4). Hence it is He, not the law, who is uniquely placed to save us. The death of this perfect God-Man on the cross for our sins effectively frees us from the bondage of the law, and opens the way for us to ″receive adoption to sonship″ (v. 5).
God who grants us sonship also makes the ″Spirit of his Son″ who ″calls out 'Abba, Father'″ (v. 6) live in our hearts, so that we might be encouraged to approach God as our heavenly Father. The Spirit's presence, therefore, is the evidence that we are God's children. And as God's children, we become God's heirs, possessing all the rights and privileges that this position brings (v. 7). Hence, in the light of this understanding, how could anyone ever want to return to the old order of the law (or pagan worship and rites) and be enslaved again?
What an incredible blessing: from bondage to freedom, and slave to heir! In Christ, believers have indeed come of age: they are no longer slaves under supervision, but mature children and heirs of God. They live in the liberty of Christ, experiencing the care of God their Father and the power of the indwelling Holy Spirit.