Till then Abraham had no other thought than that Ishmael should be his heir. But this could not be: (1) because he was slave-born; and the slave abideth not in the house for ever: (2) because he was a child of the flesh, and not the direct gift of God. Abraham had been left to wait till the hope of children had become as remote from him as it had been for years from his wife; so that the heir should be evidently the creation of the Almighty God, whose name was disclosed, ere this astounding announcement was made. This is why we are kept waiting till all human and natural hope has died from our hearts, so that God may be All in all. "And God said, Sarah thy wife shall bear thee a son indeed; and thou shalt call his name Isaac" (ver.19).
For us there is yet a crowning sweetness in the words, "I will be a God unto thee, and to thy seed"; words repeated, in Hebrews 8:10, so as certainly to include us all, if we believe. Who can unfold all the wealth of meaning of these words? All light, and no darkness at all. All love, and no shadow of change. All strength, and no sign of weakness. Beauty, sweetness, glory, majesty, all are in God, and all these will be thine and mine, if God saith to us, "I will be a God unto thee."
Nor shall this heritage be ours only: it shall belong to our children also, if we exercise Abraham's faith. God pledges Himself to be the God of our seed. But it is for us to claim the fulfillment of His pledge. Not in heart-rending cries, but in quiet, determined faith, let us ask Him to do as He has said.