Editing Pru U'Revu (Be Fruitful and Multiply) (section)

== Parameters of the Mitzvah ==
The basic obligation of the mitzvah is to have at least one son and one daughter. However, even after having a son and daughter, the obligation continues, as the Rambam rules:

"Even though a person has fulfilled the mitzvah of Pru U'Revu, there is still a rabbinical obligation not to refrain from being fruitful and multiplying as long as one has the ability, for anyone who adds one Jewish soul is considered as if they built an entire world."

This obligation is learned from the posuk in Koheles:

"In the morning sow your seed, and in the evening do not rest your hand, for you do not know which will succeed, this or that, or if both are equally good" (Koheles 11:6)

There are several possible interpretations of the obligation from this posuk in Koheles. According to the Rambam's approach, the Rebbe explains that the posuk teaches us that the same Torah obligation of "Pru U'Revu" to have a son and daughter continues from divrei kabbalah (words of tradition) even afterward, as long as one has the ability to have additional children. Having additional children, although required by divrei kabbalah, still fulfills the positive Torah commandment of Pru U'Revu.

The Gemara speaks strongly against one who intentionally nullifies this mitzvah, including Ben Azai's statement that it is "as if one spills blood."