29 And if you are Christ's, then you are Abraham's offspring, heirs according to promise.
This verse brings to a conclusion Paul's illustration drawn from Abraham's experience. It is useful to link it with 16, in order to see the line running through the whole argument. The important thing for us to see is the unity that this gives to the Old and New Testaments. We, through faith in Christ, though we be Gentiles with no connection with the Jews by birth or heredity, are Abraham's seed, and heirs according to the promise. Nothing could show more clearly the fact that from beginning to end the Bible, in spite of the amazing diversity of its writings, has one dominant theme throughout - redemption through Christ - and that however varied the surface-pattern may be, the real subject-matter is the unfolding and outworking of the divine plan of the ages, and the preparation for the manifestation of Christ as the Saviour of the world. To understand this is to hold the key not only to the Scriptures but to history and to life itself. One cannot but marvel at the grandeur of Paul's conception of the gospel. Well might he say 'This thing was not done in a corner' (Acts 26:26)! Corner indeed! It is the mighty drama of redemption played on the stage of history against the background of God's eternity. That is how big the gospel is!