Genesis 21:6

God hath made me to laugh. Sarah’s laughter a year previously had reflected cynicism and incredulity, but now she laughed for joy. The steadfastness of Abraham and Sarah through what seemed to them long, dark years of disappointment and delay, was now rewarded. To them the birth of Isaac meant the dawn of a new day (see Ps. 30:5). It was the “earnest,” or token, that the promise in its entirety — the coming of the Messiah, the gospel to all nations, and the eternal home in Canaan — would eventually be realized (Gen. 22:18; Gal. 3:16; Heb. 11:9, 10). Repeated reference is made to this glad event by Bible writers (see Isa. 54:1; 51:2, 3; Gal. 4:22-28). Like Sarah, “Jerusalem which is above,” “the mother of us all,” rejoices as children of faith are born to her today (Isa. 66:10; Luke 15:10).