In Genesis 18, Sarah overhears God telling Abraham that this time next year, she would have a son. She laughs. There is then a reaffirmation by God when, after Sarah denies her act, He says “No, but you did laugh.” (Gen 18:15)
Typically, this is read with a tone of rebuke. Sarah is lacking in faith when she shouldn’t doubt that God can turn the death of her womb into life. But is this a reprimand?
After all, Abraham himself laughs when previously told the same thing , and then points to Ishmael.
Then Abraham fell upon his face, and laughed, and said in his heart, Shall a child be born unto him that is an hundred years old? and shall Sarah, that is ninety years old, bear? And Abraham said unto God, O that Ishmael might live before thee! (Gen. 17:17,18)
Its as if Abraham thinks God is mistaken. “You misspoke, God. Ishmael is Hagar’s son, not Sarah’s. And he is right here.”
Yet there is no rebuke or other response directed at Abraham’s laughter, and as in other places, we should take notice when God himself later focuses attention.
The emphasis on Sarah’s laughing in the exchange points to something else, and we see the fulfillment after the birth of Isaac. First, Isaac’s name means “he laughs.” And then in Genesis 21:6,
And Sarah said, God hath made me to laugh, so that all that hear will laugh with me.
Sarah’s initial laughter is prophesy. It is right for her to laugh. She didn’t know it at the time, but her incredulous laughter was really the laughter of celebration. And even now, the same incredulity underlies the laughter, for Sarah asks in the next verse “Who would have said to Abraham that Sarah would nurse children?”
Part of the lesson we can learn from this is that since God is faithful to his promises, that what seems impossible becomes reality, even before our senses perceive it. When God give Abraham his new name, He speaks in the not only in future tense, talking about what he is going to do, but also in the present tense.
Neither shall thy name any more be called Abram, but thy name shall be Abraham; for a father of many nations have I made thee. (Gen. 17:5)
God declares it. And it is so. Simple as that. We should treat the promises God makes to us as good as fulfilled, and we should be even better prepared than Abraham to do so. One, the Resurrection of Christ, the climax of the fulfillment of all things, has happened. Can we think of anything that is beyond His power? And two, God has been merciful enough to give us the Spirit as a deposit or down payment, which is for us a guarantee for the future(Eph 1:13,14). He has much invested in us already, and he will complete his work (Phil 1:6).