Question:

I'm following the parsha, week by week. Last week, G‑d told Abraham he and Sarah would have a son. This week Sarah hears the news from a stranger and laughs. What's going on? Why didn't Abraham want to share the good news with her as soon as he got it?

Response:

You're obviously following it well, because you are asking the same questions that some of the classic commentators ask.

The Ramban gives two explanations.1 First he points out that Abraham knew that Sarah was also a prophet—in fact, a greater one than himself (as we discover later in this parsha, when Abraham is told, "whatever Sarah says, listen to her voice.") He understood, therefore, that if G‑d had revealed this directly to him, certainly He would also reveal it to Sarah—and so, why spoil the revelation? And in fact, we see that G‑d sent the angel Michael to announce this for Sarah—just that Sarah, since she never saw the guest, did not realize who it was that brought the news.

Next, the Ramban points out that Abraham never had a chance to tell Sarah. According to the Ramban, Abraham had just that day circumcised himself and had to also circumcise all the males of his household as well. It wouldn't be appropriate to mention in Sarah while running from one circumcision to the next, "Oh and by the way, we're having a baby boy soon."

As it turns out, from Abraham's failure to tell Sarah we can garner wise counsel about doing each thing in its proper time. Yet, there's another lesson as well. Another classic commentator, the Ran,2 cites a halacha from the Talmud: 3

Rabbi Musia, grandson of Rabbi Masia, said in the name of the Great Rabbi Musia, "From whence do we know that you have no permission to repeat anything someone tells you unless he expressly instructs you to do so? From here: 'And G‑d spoke to Moses from the tent of meeting, to say…'"4

Whenever G‑d told Moses something that was to be told to the people, He would tell him expressly to say it over. (In the Hebrew text, you'll see the word laimor. That's erroneously translated as, "saying"—which is pretty redundant. The proper translation is "to say.") If He didn't say to say, it was not to be said.

In Abraham's previous prophecies—including when he was promised many offspring (but not necessarily through Sarah)—he was told "to say"—and so he made sure to say these over to Sarah. In our case, however, that crucial word was omitted—and so he understood that Sarah was not to be told, at least not by him.

You'll find this idea discussed further in the classic work Akeidat Yitzchaak, in the Torah commentary of Rabbi Samson Raphael Hirsch and in Rabbi Moshe Feinstein's Darash Moshe.

The halacha about confidentiality is cited in the Code of Jewish Law.5 It's also a fundamental principle for all of us who work for Chabad.org/askTheRabbi.