"Paul speaks of the Mosaic covenant as a time of imprisonment (Gal 3:22-23), captivity (v23), guardianship (v24). To Paul, these restrictions leave little distinction between sonship and slavery (4:1-3). But in Christ, we become free: - 'But when the fullness of time had come, God sent forth his Son, born of woman, born under the law, to redeem those who were under the law, so that we might receive adoption as sons. And because you are sons, God has sent the Spirit of his Son into our hearts, crying, "Abba! Father!" So you are no longer a slave, but a son, and if a son, then an heir through God.' - Gal 4:4-7."
He goes on,
"The new covenant age is a time of maturity for the family. We are no longer little children, but adults, though we need to be reminded of this (Gal 4:8-11). That means that we are closer to our inheritance, the new heavens and the new earth." - Frame, ST, p114.
This is well said, but I don't think Frame goes far enough and so my postmillenial juices get flowing. Think about this. He is right. We are no longer children. We are adults. We have moved past the time of guardians to the time of taking care of the world ourselves. But what does that mean? It is not that we are "closer to our inheritance." Adults receive their inheritance when they come of age. We have received the new heavens and the new earth. They have become ours because they have all become Christ's and He has given us all things.
This is important. We are not the church in exile, waiting for God to come and free us from this dark world. We are the church triumphant, calling the nations to repentance and claiming them all in the name of Jesus. We are like the first astronaut on the moon, planting the flag and declaring the whole thing "ours!" This world is ours because this world is Christ's.