A Commentary by John Stott
This passage teaches us the scintillating glory of being a Christian believer. It involves, among others, two great privileges.
First, *we inherit the promises of the Old Testament*. The true fulfilment of the Old Testament promises is not literal but spiritual. They are fulfilled today not in the Jewish nation, as some dispensationalists hold, nor in the British or Anglo-Saxon people, as the British Israelites teach, but in Christ and in the people of Christ who believe. We Christians are Abraham’s seed, who inherit the blessing promised to his descendants (3:29). Like Isaac we are ‘children of promise’ (verse 28) and children…of the free woman’ (verse 31). We are citizens of the true Jerusalem, ‘the Jerusalem above’ (verse 26; cf.Heb.12:22; Rev.3:12; 21:2). We are ‘the Israel of God’ (Gal. 6:16) and ‘the true circumcision’ (Phil.3:3). No doubt we shall be persecuted, but all the promises of God to His people in the Old Testament become ours if we are Christ’s.
Secondly, *we experience the grace of God*, His gracious initiative to save us. We have seen that Abraham’s two sons and their two mothers stand for two covenants, the old and the new, and for the two Jerusalems, the earthly and the heavenly. We have also seen that whereas the categories of the old covenant are nature, law and bondage, the categories of the new are promise, the Spirit and freedom. What is the fundamental difference between them? It is this. The religion of Ishmael is a religion of *nature*, of what *man* can do by himself without any special intervention of God. But the religion of Isaac is a religion of *grace*, of what *God* has done and does, a religion of divine initiative and divine intervention, for Isaac was born supernaturally through a divine promise. And this is what Christianity is, not ‘natural’ religion but ‘supernatural’. The Ishmaels of this world trust in themselves that they are righteous, the Isaacs trust only in God through Jesus Christ. The Ishmaels are in bondage, because this is what self-reliance always leads to; the Isaacs enjoy freedom, because it is through faith in Christ that men are set free.
So we must seek to be like Isaac, not like Ishmael. We must put our trust in God through Jesus Christ. For only in Christ can we inherit the promises, receive the grace and enjoy the freedom of God.