Genesis 17:17-19

"Then Abraham fell upon his face and laughed, and said in his heart, Shall a child be born unto him that is a hundred years old? and shall Sarah, that is ninety years old, bear? And Abraham said unto God, Oh that Ishmael might live before thee! And God said, Nay, but Sarah thy wife shall bear thee a son; and thou shalt call his name Isaac: and I will establish my covenant with him for an everlasting covenant for his seed after him."

There is a sharp difference of opinion among scholars as to how Abraham's laughter should be understood. Morris thought that, "He laughed with joy and surprise, and not a laugh of doubt."[21] Speiser rendered it, "He smiled";[22] but there would seem to be no way to be sure. As Willis said, "It is impossible for modern man to comprehend what kind of laugh that was."[23] The uncertainty stems from the inability of translators to agree on the rendition for the words given here as, "And God said, Nay ..." If this stands, Abraham's laughter was that of incredulity and unbelief, for what he asked God was that Ishmael, and not the promised son, would be the heir; and God denied it. If that was not what Abraham meant, then God would have nothing to deny.

However, Leupold insisted that the words "And God said, Nay ..." should be read simply as "And God said to Abraham ..." thus leaving out the "Nay."[24] This corresponds with the Douay and KJV; and, if this should be followed, it would indicate that Abraham's mention of Ishmael (Genesis 17:18) was not the proposal of a substitute, but rather concern for Ishmael due to his being replaced as heir by the promised son. As long as the "Nay" stands in our version, we are almost compelled to view Abraham's laughter as in some manner reprehensible. There is, of course, a problem in that God did not at once rebuke him for it as he did Sarah's laughter in the very next chapter.

"I will establish my covenant with him (Isaac) for an everlasting covenant ..." It should never be forgotten that there were two separate elements in the Abrahamic covenant, that pertaining to the Messiah and the redemption of all mankind, and that concerning the fleshly seed of Abraham and their possession of the land of Canaan. The Messianic phase of that covenant was, of course, everlasting, for it is still in effect through the gospel of Christ. As Unger put it, "In the Messianic seed through Sarah, the kingdom would stand forever."[25]