New Defender's Study Bible Notes
4:26 Jerusalem which is above. The heavenly Jerusalem is where the Lord Jesus is even now preparing a place for us (John 14:3). It is the “city which hath foundations, whose builder and maker is God,” for which Abraham was looking as He went out into the “strange country” to which God had led him (Hebrews 11:8-10). In the allegory, Sarah represents that city of freedom in the heavens; thus all her children, with Isaac as the heir of promise representing them, are likewise heirs of the promise and therefore free.