Several anomalies occur in the story. The three messengers appear at Abraham's tent. Why didn't Abraham or one of the servants see them coming? How is it that they ask for Sarah by name? Both Abraham and Sarah are addressed by their new names, and yet Sarah doesn't seem to know that she is to have a son. In this version of the story, it is Sarah who laughs, not Abraham. Granted, she is more delicate in her laughter - she doesn't roll on the ground laughing as Abraham did. Finally one of the messengers, the one who promises a son, is identified as "the Lord." Speaking so that Sarah can overhear the promise, he tells Abraham of a son to be born in the next year.
Let's apply a little imagination between chapters 17 and 18. What if, after God speaks to Abraham as recorded in chapter 17, Abraham tells Sarah of her new name and the requirement of circumcision as a sign of the covenant, but doesn't tell her about having a son and naming him Isaac? What if 99-year-old Abraham was afraid to talk to 90-year-old Sarah about having a baby? Then we see the necessity of the visit by the three messengers to reaffirm the message to Abraham and to allow Sarah to hear it herself. Now Sarah can join her faith to Abraham's in the conception of Isaac. Abraham and Sarah both need to believe the promise.
For reflection: When has God been persistent with us in giving the same message over and over until we believe? What is the promise we have the most trouble accepting?
Let us pray. God, you are the Father of promises and the Lord of truth. Help us to recognize, understand and believe the promises you have made to us.