פרו ורבו

(28) And God blessed them; and God said unto them: ‘Be fruitful, and multiply, and replenish the earth, and subdue it; and have dominion over the fish of the sea, and over the fowl of the air, and over every living thing that creepeth upon the earth.’

(1) And God blessed Noah and his sons, and said unto them: ‘Be fruitful and multiply, and replenish the earth.

(1) The mitzvah of procreation: In parshat Bereishit there is one positive commandment and that is the mitzvah of procreation as it says (Genesis 1:28): 'And God blessed them and told them to procreate'.

(2) The root of this mitzvah (i.e the reason behind this commandment) is that the world should be settled (B.T Gittin 41b) because God wants the world to be settled as it says (Isaiah 45:18)'I did not create it for naught, but [rather] formed it for habitation'. This is a big mitzvah with which all the mitzvos are observed because [the Torah] was given to humans [who need to procreate] and not to angels [who don't].

Mishnah: Men are commanded to be fruitful and multiply-- but not women. R. Yochanan b. Baroka said: About both of them, it is said “God blessed them and said to them, ‘Be fruitful and multiply” (Gn 1:28) Gemara: From what verse do we derive that ruling? R. Ilea said in the name of R. Eleazar b. R. Simon:... The verse says “fill the land and conquer it.” (Gn 1:28) It is in men’s nature to conquer, but it is not in women’s nature to conquer.

(13) A woman is not obligated in the mitzvah of being fruitful and multiplying

(4) This [mitzvah] applies in all places and at all times (in history-not every moment of one's life) (Kidushin 36b), and a person is obligated to engage in this mitzvah when it is fitting for him and this is the age which the sages (Avot 5:21) says to marry a woman [which is age 18]. This mitzvah is not obligatory for woman. One who refrains from this mitzvah is responsible for not engaging in a positive commandment and his punishment is very great (Kiddushin 29b) because he shows that he does not want to fulfill God's will to settle the world.

(6) One may not abstain from procreation unless he [already] has children. Beit Shammai say: [One must have] two boys, and Beit Hillel say: [One must have] a boy and a girl, as it says, "Male and female He created them" (Bereishit 5:2).

(5) Once a man has had a son and a daughter, he has fulfilled the obligation to be fruitful and multiply