(55) Why did Abraham fall on his face and laugh? (#Ge 17:17). Two things are indicated by his falling on his face. One an act of adoration on account of the excess of his divine ecstacy; the other that it corresponds to and is suitable to the aforesaid harmony, by which the intellect has confessed that God alone exists in a continual and unvarying existence. But those creatures which owe their existence to creation and generation, all are subject to changes in time; for they fall to a certain extent, inasmuch as they are accustomed to rise up, and to be corrected in accordance with their original appearance. And it was very natural for Abraham to laugh at the promise, as he was then filled with the great hope that the things which he expected should be accomplished, especially because he had received a manifest revelation from that appearance, by which he became more thoroughly acquainted with him who exists for everlasting without variation, and with him also who is continually stooping and falling.
(56) Why did Abraham appear to hesitate about the promise, for the sacred writer says, He said in his mind, shall there be a son to one who is a hundred years old; and shall Sarra, who is ninety years old, bring forth a child? (#Ge 22:18). This expression, “he said in his mind,” is not added without an object or gratuitously, for words which are articulated in the tongue and the mouth incur guilt, and become liable to punishment, but those which are restrained within the mind are not liable to punishment, because the mind without any intention on its part is led away by irregularities, all kinds of passions being introduced from different quarters, which it for a while resists, being indignant at them, and wishing to keep aloof from their representations. But perhaps we should not say that he hesitated, but rather that he was struck by wonderment at the amazing nature of the gift, and so said, “Behold my body is advanced in years, and has passed the age of generation; nevertheless all things are possible to God, so that he may transmute old age into youth, and lead those who have no seed nor fruit to fertility and generation: and if a man who is a hundred years and a woman who is ninety years old become parents, all commonplace occurrences and all regularity of nature will be done away, and it will be clearly seen that it is only the power and the grace of God.”