Then Abraham fell on his face and laughed and said to himself, "Shall a child be born to a man who is a hundred years old? Shall Sarah, who is ninety years old, bear a child?"
These are words of one who in no wise doubts but is astonished and transported with joy, just as the laughter is also evidence of a heart overflowing with joy. . .. Now he forgets about his own dead body, even about corpselike Sarah, and sees with certainty that an heir is to be born to him from Sarah. . .. Abraham falls to the ground and laughs. This, as Christ explains in John 8, is the gesture of a heart that exults and overflows with joy; for now at last he is sure that he will be the father and Sarah will be the mother of Jesus Christ, the Son of God, through whom salvation and blessing will come to the entire world. Accordingly, Abraham did not fall down from fright, nor did he laugh because he had doubts about the promise; he laughed because he was filled with great gladness and joy. . .. Although we have the Word of God in such richness, our hearts are nevertheless harder than an anvil and, like rocky soil, keep the root of the Word without sap and fruit, while the saintly patriarchs marveled at this inexpressible benevolence of God to the point of being overcome. . . . Therefore we should ask God to give us a joyful heart for such joyful promises, in order that we, too, may exult and be glad with saintly Abraham because we are the people of God.