(1) ותצחק שרה, “Sarah laughed;” when the month of Tishrey began, six months after the prediction of the angels, and she had not experienced signs of pregnancy, she abandoned all hope of that prophecy becoming true, as there were only six months left for it to become true. Contrary to her husband Avraham, she had lost faith in the prediction. The reason that Avraham maintained faith in the prediction was that he had heard it from G-d directly, (the angel had spoken to him in the name of the Lord), whereas Sarah, had only been an eavesdropper, and possibly she had not heard correctly. She had assumed that the angels speaking to Avraham had been ordinary human beings. She took a look at her belly and asked mockingly whether such a belly could possibly produce a fetus. As soon as she had done so, in Tishrey, G-d asked Avraham why Sarah had reacted in such a manner, adding that at the time appointed, i.e. when a year had passed at the time of Passover, in the following year, the angel would return and she would have become a mother. In practice this means that the first time she heard the prediction she had heard it from the mouth of an angel whom she had believed to be a mortal human being. The second time Avraham heard it from G-d directly, i.e. 'ויאמר ה, “the Lord said;” this was followed by G-d adding: “Is anything impossible for the Lord to do?”Support for this interpretation can be found seeing that when the angels on the same evening met Lot, Lot offered them unleavened bread, matzot for supper, a hint that the date was the date that would later on become the night of the Seder of the Jewish people.

...[When Abraham asked Sarah to prepare bread] it was taking of bread for Passover.