V.3 The slavery to the things of this world in which we once were held.
V.5 What a contrast! Here we are redeemed, we are adopted into God’s own family and are sons. A servant is under slavery but a son is free.
V.6 Under the control of the law, we could not call God “Father.” But as free sons, we enjoy this relationship.
V.7 We are not only sons, but heirs of God. No wonder Satan wants to spoil all this by bringing us back under the law.
V.9 Paul marvels that they could be deceived and turn back again to the slavery of the law. Many believers today do the same.
V.21 In other words, “don’t you know that the law can only condemn you and curse you and pronounce the sentence of death?”
V.22-31 The story of Abraham and his sons Ishmael and Isaac. Ishmael must be cast out so that Isaac can be enjoyed as the only son. Ishmael is a picture of our old position under the law, and Isaac the son of promise, a picture of our position under grace.