When the angels came to make the announcement of Isaac's birth, Sarah laughed.

But why did Sarah laugh? If this was an announcement from the One Above (since the angels are His messengers), Sarah should have believed them. Not only that, but she should have already heard from Abraham that this was going to take place. Abraham was previously told the news that her name will no longer be Sarai, because she was soon to give birth. Why then the laughter?

...Isaac...was given a soul "from the feminine world."

Here's where the Zohar and inner dimensions of the Torah come up with some very interesting information. The Zohar tell us that the son to be born, Isaac (or Yitzchak in Hebrew, from the word meaning "laughter") was given a soul "from the feminine world."

Shem miShmuel explains that Sarah laughed because she understood that her son would have an unusual soul, based upon the precise language that the angel used. The angel said, "Sarah will have a son," and not, "Abraham will have a son." From this, Sarah understood that her son would have a feminine soul, and according to the Zohar, a soul from the "feminine world" cannot have offspring. This Sarah knew would contradict G‑d's promise that her son would continue the line of Abraham. So, Sarah believed G‑d's promise of a son, and she laughed at this particular announcement, because it sounded as if her son would have a soul from the "feminine world" and would be unable to procreate. G‑d reprimanded her, reminding her that it is not beyond His ability to change anything, even a "feminine" soul into a "masculine" soul.

And that is exactly what happened. According to the Zohar, initially Isaac wasn't capable of getting married or having children. But, at the time that Abraham offered him in sacrifice on Mt. Moriah, his soul – the soul from the "feminine world" – fled his body, and G‑d replaced it with a soul from the "masculine world." Therefore, it was precisely at this time that the Torah announced that Isaac's soul-mate, Rebecca, was born. Prior to that moment, Isaac had no soul-mate, since his soul was from the "feminine world." When his "feminine" soul was replaced by a "masculine" soul, he gained a soul-mate, as well.

We need to ascertain what exactly is a soul from the "feminine" or "masculine" world. (It obviously has nothing to do with the masculine or feminine gender, since then the opposite would be true, a female would be more likely to give birth than a male.)

...the path of the soul from the "feminine side" is to accept the world as it is...

In exploring this concept, Rabbi Menachem Mendel Schneersohn, the recent Lubavitcher Rebbe, explains that the way of a soul from the "masculine side" is to transform the world by being pro-active and outgoing, while the path of the soul from the "feminine side" is to accept the world as it is, trying to live properly according to Torah, but without trying to influence the world. Both men and women can equally apply themselves to the task of spiritual illumination of the world, each in their own way. What constitutes the difference then is not gender, but the extent to which each individual man or woman is willing to approach the task of elevation and purification of the universe.

With this explanation, we can understand what it means that Isaac initially had a soul from the "feminine world," which was exchanged at the time of his sacrifice for a soul from the "masculine world." Up to that time, Isaac's service was characterized by passivity: it only reflected his own desire to get closer to G‑d and to receive whatever G‑dly illumination would be granted to him. From such service, it wasn't to be expected that there would be "offspring" – that is, results – in the elevation of the world. After his experiences at Mt. Moriah though, his service of G‑d took on the aspect of "conquering the world," bringing spiritual illumination not only to himself but also to the universe in general. This coincided with his receiving a soul "from the masculine side." At that time, he also found his soul-mate and was able to produce "offspring" – his twin sons, Esau and Jacob.

Jacob exemplified the quest of the "masculine soul" in trying to perfect the world. His name was eventually changed to Israel because –as he was told at the time – "you have struggled with G‑d and men and have prevailed." This characteristic will forever-after be a part of his descendants, the Jewish people.

[From "Inner Lights from Jerusalem": based on the Shem miShmuel and other Chassidic and Kabalistic Sources, by Rabbi David Sterne, who also authored "Love Like Fire and Water: A Guide to Jewish Meditation.]